How is she acting during the nursing? Is she comfortable when nursing?
What are her bowel movements like? how often? what consistency?
What is your diet like? caffeine (coffee, sodas, lots of chocolate) will also cause irritablility through the nursing.
You could also try some tummy massage, very light, circular on her abdomen, during times when she is not so fussy. Or maybe it would help her when she has upset stomach too.
You could also do some baby massage. It is very comforting to baby overall. I'll look for some links. I found some recently.