It is all a bit of disaster really &she is so, so down - which is not helping
Good food, plenty of sleep, graduated approach to activities (no school, no dancing at least for the start) & blood tests in 3-4 weeks before they start blood tests
So sorry to hear this but tell her not to fret about missing dancing. She must concentrate on her health and get well first. The Royal Ballet's Lauren Cuthbertson didn't dance for over a year due to glandular fever/ME but by taking things slowly she is now back dancing principal roles.
It's not that long to half term and if she really rests now she will make a fuller recovery ... DD had a friend with glandular fever who refused to rest and she kept having problems for a LONG time after she should have been better!
Your poor DD my heart goes out to her!! While she is resting I would suggest to her that she really tries to get ahead with her school work - revision etc so that when she is well enough to dance again she can without school getting in the way. It may seem way off to her but if she has exams this summer revising now will help her balance things more easily in the exam season. My DD used to revise some topics way ahead of time because she knew she had rehearsals/classes/auditions closer to the exams when everyone else (and the teachers) would suddenly feel the pressure and start revising. It is all good practice for her organising her time. Another idea, one I'm sure she would like, read through the audition requirements/application from requirements again for next year and make a list of all those photos that will need taking in the summer and how many songs/drama pieces etc she has to learn. At least she will feel like she is doing something a bit more worthwhile with her time.