I have to disagree with the suggestion of megadosing on a particular vitamin/mineral or two. That was a strong movement some years ago (Linus Pauling was a big proponent) but it's been shown recently to cause a lot of problems and also to be dangerous.
However, the AMA has recommended that everyone supplement because 75% of the nation does not get the nutrition we need. The Physician's Desk Reference (pretty much a "Bible" on every doctor's desk) has written that absorption of vitamin pills and other pills/capsules is pretty limited - they just aren't digested in time, and they contain a lot of fillers (even waxes and shellac!) - you may remember the reports from last year about the huge number of undigested pills in the water systems and sewage filters of many major American cities. A lot of people paid for those pills but didn't absorb them, or not all of them!
Liquid nutrition has been shown to be more highly absorbable and therefore able to function at the cellular level. I know many parents of teens who use Reliv products - their kids don't get colds at all, and many daughters (and moms!) have relief from menstrual symptoms like cramping and headaches. My friend Pam has 4 kids, and one has had phenomenal relief from issues around her period. None of them has missed a day of school in well over a year, since they started on Reliv. I used to get bronchitis about 4 times a year (and it lasted for 3 weeks each time) but I haven't had it since I started on Reliv. It supports the immune system and gives us what our diets are lacking. My husband eats what the doctors call a "perfect diet" - and even so, his cholesterol dropped 40 points on Reliv, plus he hasn't had colds. So what I'm saying is, there are many results on it so your daughter may have help in many areas.
I'd be happy to share more, and my friends would be happy to talk to you as well.
Your daughter doesn't have to live this way!