That when Tiffany was getting the keys to the house, the agent called her ‘Miss Tilly’?
I don’t know if I am missing something but I find it unlikely that if that was a mistake, nobody would notice it.
It's not a mistake.
In Seed Of Chucky, Tiffany transfers her soul into the body of actress Jennifer Tilly. (Who played herself in the movie.) So now, Tiffany is posing as a famous actress, and the majority of the world believe her to still be Jennifer Tilly.
It's sort of meant as a meta-joke, I guess.