There are the foods that are common for nursing babies, dairy, nuts/peanuts, eggs and wheat. If you can, eliminate these food for 7 days, then add one food back to your diet for one meal, if you see a reaction in her, then you will know that specific food is the culprit. For example, if you get rid of eggs for 7 days, then have eggs for breakfast (no cheese though) and watch her reaction for 24 hrs, if she is gassy, fussy, etc, then you will know that eggs is a likely problem food for her. If not, then drink a glass of milk and have some yogurt the next day.
My daughter was sensitive to dairy, eggs and nuts/peanuts (and I follow a gluten-free, soy-free diet!) So I know it is not easy! However, I discovered sunflower butter to replace the nuts and just added rice protein powder to my cereal for extra protein that I was missing out on.
Also try tummy massage, starting at the right hip, moving in a clockwise position, this is the flow of the digestive system, so don't go backwards! It will help release the gas she may be experiencing.
You may also want to consider taking some probiotics for her immune and digestive system. It will definitely help and will not hurt. They do have baby probiotics which I did give to my daughter since she was born via c-section and missed out on the enzymes that they get to kick start their digestive system in the birth canal.
Best wishes!