BMYer -I apologize if I misunderstood and misjudged you.
The main thing is that she must make it clear that she is having nothing to do with him either way. Even if she wants to take your advice, she has to tell him that even if he becomes Frumer, she still will have nothing to do with him until he has spent two years in a Yeshiva, and if he really “frums out” he can contact her via a shadchan (and only via a shadchan) at that point.
I’m not even sure that’s the best idea, but if she takes your advice, that’s the only way she should even consider it.
Personally, I still think it’s a bad idea though.
In terms of the fact that nothing else has been working, that’s only because she hasn’t tried hard enough yet, because she hasn’t yet convinced herself to get rid of him. And she is still giving him rides, which she must stop, ASAP!!