Have her parents contact the school (teacher, principal, etc) and bring doctor's notes. She should be allowed to make up work that she missed due to a properly documented medical condition. Also, just because a person is absent from school does not mean that they should automatically be exempt from all assignments. With very few exceptions, a student can still complete some assignments sent home by the teacher. If she (and her parents) didn't make any attempt to find out what work she missed and what she could do while in bed to try and keep up, then there may be issues. Also, if a student misses a certain number of class periods of a class around here- REGARDLESS of the reason, medical or not- they will not be able to pass the class. If you have an extended illness then that's really an unfortunate thing, but in reality the chances that you've gotten everything you can out of the course while not being present most of the time is unlikely. Don't know if your friend has exceeded the number of absent days, but I guess it's possible.
Though, I don't think that you're the one in the position to be fighting this battle.