Do you leave her on the spot? Once a cheater, always a cheater.

Yes you should vet her before committing but such things might surface long after that, when the "sunken cost fallacy" has already kicked in.

I'm also aware that girls tend to be serial monogamists with branch swinging from a relationship to another but such behavior was unacceptable a few decades ago for obvious reasons and Feminism has normalized it even though it's unhealthy as hell.