It would seem to me that she is using her illness as an excuse not to participate in school.  It seems to me most CAH children do not have any CAH related problems in school,  not to say that when the children do get sick they do need extra medical attention.

My CAH children although younger participate in all sports, swimming, running and tennis. They also do very well in school and maybe miss a day a year due to illness.  She should not be missing so much school if she is getting good medical and care and is under good control, which can be difficult during puberty.

There maybe some physical differences in the young female CAH patient depending if she is virlilized and maybe that is why she does not want to get dressed or undressed in fron of other teenagers?  It sounds like this young women is having some real issues. 

Just a couple of thoughts.

Good luck to you.