Could be a White Plymouth Rock (also called White Rock).
There are other white breeds that lay brown eggs, but I think that's the most common one.
Details I looked at when trying to figure out breed:
feather color (white)
egg color (brown)
comb type (single)
leg color (yellow)
earlobe color (red)
Features some breeds have that she does not:
extra toes (4 is normal, a few breeds have 5)
extra feathers on feet and lower legs, crest on top of head, muff/beard feathers on face