Sugar is not poison, think about the diabetics that need sugar, when their count is dangerously low, its like a life line for them... so much for you being a student in medicine. Your body naturally processes it as long as its moderation, that's the key.
As for being nauseated every month, you can't really say if she has a poor immune system, you have not gone over her medical records, all you can truly say is that you recommend she talk to her doctor, maybe there might be a iron deviancy, or low blood count otherwise, you just never know.
You studying medicine should right away not to diagnose, or let alone throw medical advice out there, you should only advise seeking a professionals help, nothing more.
I am a student of natural medicine and if you are getting sick then it is because you have a poor immune system - which is obvious - a few things that might help is to 1st stop eating sugar - it is poison - try substitutes - there are many.
Try searching through this website - it is very informative and you will enjoy learning about the products. I suggest as a boost to your system right away Goji Berries! and Echinacea tea/ginger minced with water and hony is alo excellent - just gotta get over the taste and another great idea is a colon cleanse when you are a but stronger
try the bottom 2 links - i buy through this website as i get cashback and they are great to deal with.