For all of us who work with human beings, our humility brings us always back to: First, do no harm. Sometimes that's hard. Sometimes we make mistakes, notice things we wish we'd known before, or had been able to handle or perform better.
Don't insist a student take a pose s/he doesn't want to do. Don't ask twice. Respect your students' body wisdom. Become unattached to that teacher/student hierarchy. Teach your students to trust themselves. That's how they'll make friends with their bodies. That's how they'll heal.
Even more impressive than the power of yoga in this story is the fierce resiliency of these teens' spirits. Perhaps yoga and meditation awaken something in the human spirit that was always there, but which we lose sight of or neglect.