No, I do not believe that it is possible under normal circumstances. From what I know about the HIV virus, it cannot live outside of the human body for long. Unless she sits on a large puddle of fresh blood on the seat that was recently left there (Not that she would! She would see it) she doesn't have anything to worry about. Even if that doubtful situation happens, it has to enter through a cut or sore on her body. So again, NO! This cannot happen. If you're concerned about hygiene, get her some travel toilet seat covers. You can get them at Walmart where you find the travel-sized stuff. That way, she can use public toilets with a bit less worry. With that being said, recent research has shown that it is actually SAFER to sit directly on the seat, with no cover. I am serious. Google it if you wish. Squatting can cause splashing, and the covers are also not great. Doorknobs and floors in the bathroom are much more unsanitary than the seats. They are not cleaned as often. Anyways, I hope this clears your doubts. Best wishes!