HUGE ISSUE.
TOOOOOOO MANY UNKNOWNS TO DECIDE. I'd want a detached-from-family memer--a therapist to explore that issue. Also a trusted friend or 3 to explore it with the daughter.
It COULD make it worse to do what you suggest. CONTROL is a big issue. If the daughter wants to stay in that school and is forced to leave--it would cause her to feel EVEN MORE OUT OF CONTROL AND EVEN MORE COMPELLED TO CONTROL/LIMIT her food intake.
Thanks. Many people have suggested we yank her out of school at once. That may be the course we take, but the professionals we have consulted with already have echoed your thought: That making her quit her school (where she does well, has friends, and absolutely loves it there), could really push her over the edge.
If it comes to that, it comes to that. But if there's a way into treatment without that (for example, her school's health department is ready to jump into her treatment), we'll go that way.