My neighbor is blaming me for poop on her doorstep?

The girl who lives in the apartment down from me thinks that my dog keeps pooping on her front step. It isn't my dog because she is always on a leash and I see wherever she relieves herself, plus I would never let my dog to that to a neighbor. There are a lot of dogs in the complex but I guess she blames me because I'm the closest with a dog. She knocked on my door the other night and was very angry and confrontational. She demanded that I clean it up. I was pretty nice and calm about it but she was really mean. I ured her it was not my dog but she wasn't having it. The mystery dog keeps pooping in her doorstep and she always peers at me out of her window when I take my dog out. Can she get me in trouble with animal control/my apt complex even though she has not proof it was me? How can I resolve this?