What it sounds like to me is Bacterial Vaginosis (BV).

Bacterial vaginosis (BV) is the name of a condition in women where the normal balance of bacteria in the vagina is disrupted and replaced by an overgrowth of bacteria. It is sometimes accompanied by discharge, odor, pain, itching, or burning, and it can be painful during intercourse.

If you have seen doctors and they keep misdiagnosing her and none of them have mentioned (BV) I wouls ask to have a test done. There are also a few other vaginal infections she could get tested very easily for to rule them out but her symptoms sounnd very much like (BV).