ask her calmly: "what are you really mad about?/what's REALLY bothering you?" and don't make it to be about you or her harping on you. Make sure she feels that you can see through the BS complaining and want to get to the root of her problem. If she doesn't stop and answer you then there could be a few things going on. 1-she doesn't know how to end your relationship so she's trying to make you end it with her first. 2-she's been holding in her true feelings about something you did to her a long time ago and it's starting to explode out of her. 3-she just really doesn't like you anymore.

I should also a bit more concise about my advice~you can't 'fix her attitude' without expecting to take some responsibility for it. relationships are hard work, everyone knows that. But you are married so you should work harder than the unmarried. She's clearly upset about something you did and it's more likely that she hasn't told you about 'what' yet and just doesn't know how. Be patient with her and try to let her know that you're willing to help her figure it out and resolve it... without just accusing her of having a 'horrible' attitude. Something's going on-period-and you can probably guess that it's not the little things she's actually yelling about. be prepared for some potentially highly-intense communication!! Then work with her to move past it and get back to a calm, loving place... like when you were inspired to marry her.