One of my favorite movies of all time, Young Frankenstein, had a scene with Abby Normal. Igor was sent for the brain of a genius, but he dropped it, so he got another. He couldn't read, so the fact that it was "abnormal" was not clear to him. When it became clear that the brain was not actually that of the genius, he admitted it was from someone else. Ab... abby.. Abby Normal.
It's entered common vernacular. It's just a funny way to say "abnormal."
She's not normal.