I don't think it's fair to point to her relationship as the cause of this. I also think that, referring to her relationship as "banging a co-worker", may be an example of the kind of behaviour that creates an uncomfortable atmosphere for women in I.T.
She was engaging in a personal relationship with the founder's spouse as well as a sexual relationship with a coworker. How is that not asking for jealousy related drama ? Does it really matter how that drama eventually manifests ? I don't think so.
I'm just trying to hold her to the same standards that a male would be held to.