Rude lady!
This why I try not to even mention anyone's weight. Not even to say "are you losing"? I'm not sure what her real "motives" were, however I do know that in the mind of some...if you are not "instantaneously skinny", then they don't necessarily think that you had surgery. I'm still a relatively "heavy weight" and I'm more than 1 year out. The only reason why some folks noticed, is that I carried a lot of the weight in my face, breast, and stomach. Although I'm sure folks noticed...I can GUARANTEE that they wouldn't think for one minute that I'm down 122 pounds from my highest weight.
I know that some folks are more sensitive than others, but since you are saying that she's "real big herself", I really would try my best not to let it bother me. Folks will say all sorts of stuff that's not necessarily "warm and fuzzy" throughout this journey.