Your cake was fine. But this will happen again if you continue to leave cake with anybody that's crass enough to be that nasty. She'll tell all of her nasty friends... "Guess what! I figured out how to get free cake. All you have to do is..." And you know the rest of the story.
We all need shirts that on the front say, "Don't like it? Then,." On the back they'd say, "NO CAKE FOR YOU!!" I swear we wouldn't have half the problems.
Chin up and don't listen to the witch with a "b." Continue to make cakes because you like to and you're good at it, not because some crass in-duh-vidual doesn't know a good cake when she sees one.