What kind of person does that to a suicidal teenager?! Many people who don't really intend to kill themselves end up accidentally doing it anyway because they screw up.
That part made perfect sense to me. Watching this girl was taking resources away, and if she was determined to kill herself, it was GOING to happen. No one can watch her 24/7, she'd find a free moment. This was just focring the issue, the 'shit or get off the pot' moment. Either she does it, and the group can stop wasting time and manpower, or she realizes she wants to live, and it's over.
Having been in a similar situation, she probably realized that it wasn't going to resolve itself until she really had the opportunity to DO it, and then she'd see whether she REALLY wanted to, or if she wanted to live...