My girlfriend and i have been together for a few years, and are pretty sexually active. But lately (the past few months or so) her "down there" has been smelling super off. Very fishy and not at all like the normal smell im used to. Every time i bring it up, she gets really upset and defensive. And ive not been rude about it. For two months. I dont know what to do, but i cant go down on her any more and i have to wash my hands right after sex. Its that bad. She threatens to break up with me if i bring it up again, but then wants to have sex and share toys Which im scared to do because i dont want to spread whatever it is. What do i do??

Edit: shes a nurse. So she knows what it would be, just denies and absolutely refuses to consider that there is a problem at all.