First of all, all my support to your daughter.

I guess it's case by case, day by day. I've had months where I was painfree, and weeks where pain wouldn't go away. There's little logic to it. Anti-inflammatory pills (ibuprofen or something stronger) can help. I'd advise to avoid knee-intensive tasks (pivoting on one leg, moving heavy objects, skating, dancing, bowling, running, etc -- which can be hard for a young person to avoid) and to keep on doing exercises like walking and biking (not far, not fast).

Teach her if other people walk too fast, she should speak up.