I'd start out by just getting her into the cross ties and grooming her, especially around the girth area. Let her know that just because she is there does not mean pain is coming next. If she acts nasty because she's afraid you'll hurt her, make sure you are out of range so she can't do anything to you and then ignore the behavior, but keep brushing. Once she settles, THEN stop and put her away. Do this for however long it takes her to realize you aren't going to hurt her, and then gradually increase the pressure by girthing her loosely, and stopping with that for a while. Once she doesn't pay you much mind fasten her up loosely, then groom for a few minutes, then tighten the girth up a hole or two. It may take a while to overcome it, but if you move slowly and give her time, she should get over it. Of course that will mean you can't just toss a saddle on and go riding for a while. Maybe bareback or something of that sort for a while if you must. But it will be worth it for her to not anticipate pain with tacking. And the important thing is, once you do get her straightened out, use a girth that fits and take it up slowly, not all at once.
^^ Ignoring her will only make the biting worse. Do NOT ignore a horse who bites.
Say "no" in a loud and firm voice. Jerk his lead line (Not extremely hard, but hard enough to get his attention and let him know he's done something wrong.)
As someone else said, brush and pet her a lot in the girth area, this will let her know that you are not always out to hurt her.
I was watching a Dennis Reis episode, and he was talking about a stallion who had a huge biting problem. He took him into a round pen and did whatever he could to the stallion that would set him off. Every time the stallion tried to bite at him, he would make him work.
Back him up, make him do side-steps, send him cantering in a circle. Make him work hard, and breath heavy. When you think he's had enough bring him back to you, pet him and start over.
It takes time, but a biting horse should not be ignored.
Edit: I apologize for using "he." Oops. (: