People fraudulently sign petitions all the time. That is why they go through a vetting process by the Sec of State - when they are official petitions. So unless they can show that she knowingly put fraudulent signatures on it, big whoop.
I don’t know if this petition had any legal value, it seemed by my skimming of the story it was just a “sense of the people” type thing. But I could be wrong. But I suppose once it was handed over, it became official business.
Or maybe, they slipped it in her folder when she wasn't looking.
Actually, I'm thinking this is more likely. How else would the mayor know she had it in her folder?