J.M.
go to the doctor immediately. esp since its summer, there is a very high chance she could have some degree of dehydration. after that is looked at, figure out whats going on.
im not sure if this is an illness like a stomach bug or you mean this is an ongoing problem. either way, the doctor should figure out what it is. if its ongoing, it might be something serious, so dont delay. if you are saying she doesnt eat properly to begin with, i assume you mean she doesnt eat an appropriate amount for her age, if so, i would def get this taken care of because the reason she vomits may be the reason for her not wanting to eat. its not good when young kids lose weight, big red flag.