I don't understand this, could you explain
She fucked a bloke who fucked a barebacker, and as a result he thinks she's medically risky to see. There's also an unsaid implication that he thinks she may be a closet barebacker (or in bugchaser terminology, UTC - under the counter).
Whether there is really a risk is a secret between the girl and her GP, in the meantime consider the risks as you see them and ensure appropriate protection before fucking her