Hmm, she's got a violent husband, but didn't call you to beg you not to tell him, but to goad you and wind you up further. She's got a husband any 'normal' woman would be terrified of, but she's not afraid of further inflaming the situation by insulting you and making you angry at her.
I'm calling bollocks about the violent husband. or rather, I'm calling bollocks that the OW has to fear his reaction - she is not acting like a woman in an abusive relationship who was looking for an exit route. Your 'D'H might well have a lot to fear from the OW's husband finding out, but her, nope, don't believe it, or rather, she doesn't believe she has to worry.
Calling you does make her seem like a woman scorned, that your DH has been filling her head with lies, convincing her that you are so terrible and of course it's perfectly natural that someone in such a 'terrible' relationship would stray, gosh what a saint to have put up with you so long...
so she's angry now, because she had a relationship with your 'D'H based on his lies.
To me, it sounds like your DH is trying to keep a lid on it, reduce the damage he's caused in his own life. Right now, it's just you that knows, he's not having to deal with his OW's marriage breaking down, it's not public, he doesn't have to worry about the fall out at work from having an affair with a colleague, a lot of companies have policies against relationships in the office, and even those who don't, it could make him the office joke...