If your horse is girthy, take your time girthing up and walk her after tightening a hole at a time. You could also try a different style of girth, maybe one with sheepskin or memory foam. You may also want to look into why she is doing this behaviour. Is she in pain? As biting during the saddling up process is usually a result of pain. Have you had her checked for ulcers? Does she throw and chuck her head around while being saddled? These are all signs of gut pains.
Hopefully there is nothing wrong with her and she just doesn't like the girth being pulled tight.