What might cause a child to get strep throat very often? my daughter has had it multiple times (up to 3-4x) per year for the past several years?

She is likely to be a strep carrier. Adequate treatment of carrier status requires injection of benzathine penicillin or combination of antibiotics.

Depending on the season an estimated 10-30% of persons can carry strep in their throat and not be ill. If a throat culture/strep test are done during another illness (viral) they will have a positive test, but lab tests later would indicate they were not infected by strep. Special treatments can end the carriage state, but it can return.