Damn, im sorry for what both of you are going through, sounds like a difficult situation and if I were in your shoes I probably wouldn't know what to do either.

I agree that her moving in with her parents doesn't seem to be in her best interest from what you've told us.

A few things im curious about is, is she still in counselling/therapy? If yes, did she bring up the concerns she shared with you to her counselor/therapist? If not, im guessing theres a good reason for that. Would she be interested in resuming therapy?

Also, im just curious is there a reason she's restricting herself to those 2 options? Are there no others available? Like moving in with roommates, or perhaps staying with you a bit longer? If of course you'd be fine with that. But im guessing she wants to move on cause the break up is still a bit fresh?

As to what you can do, well, from my perspective there isn't much you can do. You can give advice, listen, validate her feelings, express your concerns, maybe even try as hard as you can to dissuade her from a certain action etc, but ultimately she could end up going back home despite what you and the therapist have said. In which case, all you can do is be a supportive friend.