Do they know you are an Atheist as well? If so, why don't you take advantage of the situation to educate them on the subject by comparing her behavior to yours and making them to see the difference?

Point out all of the religious sexual predators, spouse abusers, and hate mongers who have been actually convicted of crimes. Then posit that it isn't her beliefs that inform her behavior because if that was the case there would be no such thing as religious criminals and predators. Moral debates typically never end with an agreement, but if you provide evidence to refute their reasoning, even if it doesn't register immediately, it will eventually, and they will be a little less judgmental until it's convenient for them to forget again. It's really a battle of attrition.

Just comment that fanatics are messed up no matter what their beliefs are, as there are many more people who are messed up who are religious. Most atheists whoi are messed up, got messed up via a religious upbringing. I've never heard of a religious person beign messed up due to an atheist upbringing.

Just a couple of points to throw out there.

I saw a great meme about this, it went something like this:

[defense against some ignorant personal behavior] sorry, i'm a scorpio and we're just like this.

No, Karen, you're just a BITCH. lol.

Tell her what an ass she is, and avoid her.

I definitely sympathize. I've built up trust at work and also represent atheism in a positive way. Most people I know well identify atheism with me. Some are also atheist but not many. Most of them do not know who else is an atheist among them. So when a "bad apple" atheist comes along they don't see it as representative of atheism. If they don't have that "good apple" example, they will associate her behavior with atheism. That is why it is important to speak up and against the bad behavior at the same time as you identify yourself as non-theist. Break the stereotype that they have.

Her behavior reflects solely on her and not on all atheists. If theists around you make assumptions and generalize, that's their problem.

I don't know anyone like that, but i have a little rule that applies to atheist, theist, women, men, black or white.
"Life is too short to spend it in assholes."
So live your life as better as you can and do not waste time in people who does not deserves it.
Cheers!