Can you pull her out of school? Empty the house of everything you could feel has the slightest risk attached to it, and have someone with her around the clock? For now, that is what I would do personally. We would even have her in bed with me.
I would set up a programme of running every day (with her)
walking
Buy a pet for her to take care of
Healthy foods
Meditation everyday
Breathing techniques
Talk and talk, try to uncover where the root is for her
Put flowers and plants in her room, ask her to water them
Take her wild swimming once a week
Ask her friends to come over every week for dinner, movie
Stop SM altogether.
I think you need to get the big guns out, and do something really really drastic. Even in the worst case she still found a way, you will know you have done everything possible.
I would not trust the school, any school to stay on top of this op.
I say this as someone in a similar place as a teen, do not give up and listen to CAHMS - there is ALWAYS much that can be done, always because she is your child, and you do what you need to.
She may not always stay like this, in my case it lifted naturally around 19 years old. So sorry op
I can't imagine what you are going through. Make sure you get some support for yourself as well.