OP, wishing you the best. Such a hard place to be in.
I have had a couple of friends whose kids have had to take time off from college to recover their mental health. It is so tough to watch your kid struggle.
Just a couple of thoughts…
If your D is not likely to harm herself, the farm could be great. She will be outdoors, physically engaged, and have activities and goals that may be more immediate and visible. She will be around people who are different from here and seeing different paths to happiness. It is entirely possible that she knows in her gut that this is the re-set she needs to recover from the situation that has made her unhappy. If this works, she may also recover some confidence in her ability to choose what’s right for her. I understand your fear. But if it is not for her life, this may be great.
On meds, a dear friend who suffers from bipolar disorder said “there’s a reason they call it practicing medicine”. Meds really can take a lot of tinkering to get right. It’s not unusual for someone to decide they don’t want this after a bad start. I’d encourage another try. But if she wants to wait until after the farm, maybe let her have that control.
You are dealing with a lot here! You need to have strength, patience, and clarity to support your D. Get your own therapist as part of your self-care. You are asking too much of yourself to take on the worry, the doubt, the heartbreak alone. This is undoubtedly affecting how you deal with your D, the family, etc. You need someone who is solidly there for you. You might also be setting a good example for your D.
Lastly, I really hope that this part of the journey leads you not simply to no longer depressed but to joy and peace.