You are not small at all! And like others have said, just ignore her. She's trying to do that to get back at you.
I've had the same exact thing that happened to you happen to me. I started dating a new girl and my ex felt the need to go to her and say "his dick is small and extremely curved to the left" (no idea where she even came up with that) before we had sex.
Needless to say, my new gf was pleasantly surprised when she found out that wasn't true and she went back and told my ex that she needed to put a sock in it! (probably in much more colorful language) :wink: