There could be many things causing this. Yes, lactose intolerance could be one but that should be looked into a little later. My son is and always has been a very "spitty" baby. My wife and I tried a number of different formulas until we found one which cut down of the amount of spit-up (I'm not sure you can avoid it entirely). He did the worst with Enfamil and the best with Similac (must be something with those "comfort proteins). Try switching her formula (doing so gradually over about a week) to something else. If that doesn't work, there are other versions of these formulas which may help. For example, Enfamil has "A.R." for spitty babies. It is thickened with rice starch (a thicker solution tends to help with spitting).
Try visiting the
Enfamil and
Similac websites. Compare the types and see what you and your wife think with help.