I don't think you will know for sure until she is old enough to have the tests done.
My son Lucian has a suspected dairy allergy, that he has inherited from me. I was eating dairy during my pregnancy, as the hormones were masking my allergic reaction (itchy hives all over my body).
I still continued eating dairy for a couple of weeks after I had him. He was diagnosed with reflux, and I immediately cut the dairy out my diet, as I was starting to react again. His spilling has decreased dramatically, and is virtually non-exsistant now.
My GP and a paed told me to wait till Lucian is a year old before getting tests done, just to confirm it.
If she has a dairy intolerance, a lactose-free formula won't make a difference (as it is made from cow's milk), unless she is also intolerant to lactose. For me, I can easily tolerate lactose in food, but am allergic to specific proteins in cow's milk.
Hopefully you can get some answers soon.
I would also highly recommend the Crying Over Spilt Milk website for info on reflux and food allergies:
Linky