Heavy Hair Fall, Tiredness Post Treatment For Gland Fever. Measures To Improve Immunity?

Dear Doctor, my daughter had gland fever recently. How do we go about preventing such a occurence again. She is much better but now is losing her hair . Could this be because of the fever and the fact that did nt eat and drank water and medication for pain and fever aswell as the anti biotica. She could not swallow as her throught was very sore. She is a very active in sport, playing tennis, action hockey and gym . So I do understand that she is frustrated not participating any of it now. She started to practice some slight gym cessions, but get tired very quickly. Maybe there is some kind of Vitamins and minerals that she can use to help with immunity? Thank you for attenting to by query. Kind regards, Anna-Marie