As others have said,
It -can- work, if you both want it to. Seems like that's in question at the moment. You need to resolve this one way or the other first of all.
There's a chance that this could be the kick up the arse that you both need to buck your ideas up and remember why you're together, and to stop taking each other for granted. I'd disagree with the notion that "she's done it once, she'll do it again"; as someone else said, I'd suggest that this is a symptom of a problem, not a cause. Fix the right problem.
To be honest though, from what you've said it does sound like she's not interested. For it to work, you both have to commit to fixing things, otherwise she absolutely will stray again, it's just a matter of time. It's not enough just for you to forgive, and the onus shouldn't be on you alone to sort this out.
My gut feeling on this (as a random bloke on the other end of the Internet and therefore an expert) is that you should be giving very real consideration to the idea of kicking her out and moving on. Not for the infidelity, but for what essentially sounds like the contempt she has for you. It's easy to get complacent or distracted and anyone can make a mistake, but then to be not just unapologetic but actively distraught that it didn't work out is just downright callous. That's the showstopper for me, right there.
