I don't know if this will help but Pervy gets those when I don't treat for fleas soon enough. I think she reacts badly to even one flea. She chews and grooms so much that she will make a blister on her lower lip. As soon as I pop on the Advantage her blister goes away! It looks exactly like Princess's lip. I don't know if that is what is wrong with Princess but I thought I would let you know that with Pervy it isn't anything horrible.
Pervy is my little flea monitor!!
Keep us posted!