OP- hug. This sounds terrible.
Even though you don’t want your D to be ratcheting back and forth like a ping pong ball- sounds to me that she needs to understand that if she does nothing, she is not going to college in August. Not this college, nor any other.
That’s reality. Next move is hers.
Your ex-wife can get a court order but garnishing your (non existent?) wages-- which I don’t think is even a remote possibility- still doesn’t get her tuition paid in August.
I don’t know where you live but in my state judges are increasingly leery of women who fail to “relaunch” financially after a divorce. Yes- it’s sexist. But a family court judge isn’t a millionaire, and they are often women. They wake up every day and put on their robes and head off to work- while balancing everything else as well. I have a friend who ended up with a generous settlement (by any reasonable standard) but not as much as her lawyer had claimed she needed and the judge told her in open court, “you need to get a job. You speak English. You are not an illegal immigrant. You have a HS diploma (she has a college degree but this was for the sake of drama). So you need to get a job. Next time you appear with a frivolous filing about increasing your support, I need a paystub from your job before I will consider an amendment. Next case”.
So I think you need to tell your D- “either you and your mom cooperate, or you don’t go to college this year. What’s plan B and how can I help get you there?”