NO
This girl sounds like a total nightmare and is quite frankly emotionally abusing your son. I have to be honest and say I would have an extremely hard time not offering my help given the history. Do you know the family or the parents? Could they be of some assistance here? Sounds ridiculous but I would want that stuffed animal from his childhood back and would not allow something of that value to be “thrown in the trash.” That statement says to me she is intentionally trying to hurt or demoralize your son and it appears to be effecting his emotional health.
I would talk to your son and see if he thinks you can somehow assist with the situation. I would do nothing without his approval but if he gives you the green light I would make the call and communicate quite clearly that her actions are not appreciated. I would ask for the childhood memento back.
I imagine your son is feeling pretty dismal and just may not be able to fight his own corner right now. At the very least your offer to help will make him feel supported and loved. I agree that going forward the girl would not be welcome in my home.
Writing this through big tears—thank you all for the kind support. I do not want to bash this girl in our community, which is why I came here. Her family situation is difficult. I would never call her (separated) parents, who have restraining orders against one another. I think her unstable family life feeds the drama. Nevertheless, my son was indeed foolish to give her such an expensive gift. His stuffed moose going in the trash though… that is what hurts the most, and it’s not about $ but sentimental value. He is 17, almost 18. Many hard lessons to be learned, but I think I will heed the advice to give him love, support, and guidance but otherwise stay out of it.
Her parents have restraining orders against each other? No wonder she’s a bit of a mess, and doesn’t know how to conduct a mutually respectful relationship. Very sad all round.
I think my daughter might have sounded like a mean or petty girl if described by her boyfriend or boyfriend’s father when she broke up with him (twice) just after spending vacations with his family. Um, maybe she broke up with him (twice) BECAUSE she spent vacations with him. They looked at it as her ‘using’ them for the vacation. She viewed it as “OMG, I couldn’t stand another minute with him or his parents!” I was sort of in the middle and questioned why she even wanted to go on the vacations with him in the first place, told her to be nice, but she was an 18 year old and probably wasn’t nice. The father had called me in the spring telling me of ‘their’ plan to come to daughter’s graduation (we lived in Florida, them in Calif), go on vacation in Florida for 2 weeks, drive across the country to my daughter’s orientation at college (Wy), drive to my niece’s wedding in Washington, and have her spend the rest of the summer with them in California. No, not going to happen. So we settled on graduation and one week of vacation. Daughter then broke up with the boyfriend and she was seen as mean and he wanted all his stuff back, plus $200 for a trip she’d taken to visit him 2 months earlier. I packaged the stuff and paid the $200.
We saw this guy last year at a mutual friend’s wedding. I know he’s still pining for my daughter and the life he could have had. Really, the return of his stuff didn’t help him get over it. I don’t think my daughter is mean or petty. I think she is a kid, and kids say mean and petty things when they break up.
Honestly, to me this sounds downright weird.
@twoinanddone your scenario is very different than what was described in the original post, much of which I found to be intentionally cruel. But from what I can gather from the additional info in post #22 the girl has other battles she is fighting. I understand the OP’s desire to tread lightly.
But if it were my S, I would turn my respectable self into a “trash picker” for an evening and get him that stuffed moose back. 
My oldest dated a girl like that for a little over a year. Don’t contact the family or the girl. It’s possible she won’t carry through with her threats and he may be able to get it back when some time has passed, or he may realize it’s a small price to pay for his freedom.
If you still have some control over your son’s health care while he is 17, can you talk to his doctor about suggesting a couple of counseling sessions with a psychologist specializing in teen issues? He might reject the idea or he might be willing to go, but I do not think there is harm in asking. It sounds like in the past you already hinted to him that getting back with the girl was not such a great idea. Sometimes hearing the same thing from a different person makes a world of difference.
Love that quote @yucca10!
Hugs OP.
I have a romantic son who has had his heart broken a few times in his short life. Stuff was not involved. (Okay, one girl dramatically brought him back a box of all the gifts he had ever given her. The opposite of your problem.) I made myself available to listen. I have been relieved that he has behaved well, not been obsessed and pining, nor wanting to hurt the girls back.
This is just hard stuff that young adults have to go through. With my S, I have been proud that he dusts himself off and gets back out there.
In addition to all the good advice here, I’d suggest talking to your son about always “taking the high road” in a breakup. He can’t control the girl’s behavior - and make him understand that she is a product of her environment, and therefore deserving of some sympathy - but that he deserves better and that means no longer subjecting himself to this girl. But, no bashing or trash talking from you, from him. Even though he is surely upset about how things have gone, by taking the high road he can walk away from the relationship holding his head high, knowing he didn’t contribute to the ugliness and that will serve him well for forming healthier relationships in the future.
I know how tough it is as I’ve gone through it several times with my kids. Hugs.
OP, the girl sounds a lot like my high school boyfriend (that I dated for far too long- 5 years). Her parents were never together and they were both abusive towards their new SOs, to my ex, and to his siblings. When they weren’t abusive, they were just negligent. His dad kicked him out on Christmas Eve right after he turned 17 because he needed to make space for his new wife.
It took me years after the break up to realize that he was, in a way, emotionally abusive towards me. I paid for a lot of his things and I’m sure I “lost” a lot of money in the relationship. But I harbor no ill will towards him because he just had no idea how to be in a healthy relationship.
All of this is to say that my parents, bless them, never tried to intervene. They were always there for me and if anything had gotten bad, they would have stepped in. It never reached that point and because of that, I always knew I could turn to them. I still don’t know how they bit their tongues but I’m grateful that they did.
Honestly… if it were my kid’s beloved stuffed toy, Id call the girl myself or knock on her door for it. Doesn’t sound like she has parents who will tell her right from wrong. And I’d tell my kid in no uncertain terms to stay away from her for good.
The father was/is weird. They’d dated long distance for two years (we used to live in Calif and they’d gone to the same high school when she was a freshman). The father kept calling me to set up visits, but then he wanted her to spend the summer because he had a business and she could work there and they (the kids) could ‘really get to know each other to see if this would work.’ I didn’t even want it to work. I kept saying “She’s 18, she’s going to college, they aren’t getting married. They don’t need to make it work right now” I actually agreed to it when he first called me because he said they’d all discussed it and that’s what my daughter wanted (she’d just been there on a vacation). Then I yelled at her, then she cried that it wasn’t what she wanted, then I thought “Hell no” and called him and told him. He was really mad that I wanted my daughter to live at home for her last summer. Of course then they came for graduation a month later and daughter broke up with son a week after that. Really, a lovely memory!
It was really a case of the BF being an only child and always getting his own way. He wanted my daughter to be his GF, and the father was getting that for him. The mother was nice.
But the OP girlfriend isn’t a monster. She’s an emotional 17 year old kid. Something didn’t go right and she lashed out with what she knew would hurt, not returning the gifts and threatening to put them in the trash. I suspect if OP called and asked her for the stuff it would be returned. I also suspect that everyone at school would hear about “Mommy” asking for his toys back. We’re not dealing with a mature set of people here, but I’ve adults argue about less in divorce court, when they are paying divorce lawyers to get back the stuffed moose, the vacuum cleaner, the art work they bought on a vacation…
@twoinanddone, that father’s behavior was “RED FLAG” weird.
^^ I do think it is important to talk to teens about the difference in dating and marriage/prepping for marriage. I’ve expressed to my teens that dating and being very fond of someone is fine, but they need to make sure they are making decisions that are best for them at this point in their lives.
To be honest, BF would have married her if she would have said yes and they would have absorbed her into their little family. And if I hadn’t been there saying ‘you are going to college’ she might have said yes. She has several friends who have married young and thinks their lives are just perfect. The wedding we attended where we saw the old BF was between another high school friend and a 21 year old bride. This guy had asked my daughter out in high school too. Daughter’s best friend is Mormon and got married weeks after her 21st birthday, before finishing college, because she wanted to be married. Another hs friend had a big wedding after waiting for her boyfriend to serve two years in the marines. It all looks wonderful and fun and romantic to my daughter. Much better than waiting tables and going to school and sometimes not having a fun life.
Other daughter has been dating a guy for 3 years. He graduated last year and moved back home. She’s evacuated to his house in NJ for Hurricane Irma (which might be a permanent evacuation looking at the maps of Florida) but I have no fear of her getting married. She doesn’t want to live in NJ near his mother, high school friends, brothers, 9 uncles and assorted relatives! She doesn’t want to relive his high school life for the rest of her life.
I would get that stuffed animal back no matter what it took.
Why the heck did the OP’s son give a girlfriend a stuffed animal if it was that cherished? I don’t get it. He presumably was willing to part with it…
The most worrisome thing to me would be the son’s willingness to go back to an immature, vindictive girlfriend more than once. That is the biggest red flag I see.