Alli probably invited herself to this party, or took Britney's invitation, and then called the paps, saying something like "Paris Hilton will be at this location..." to ensure that she would be photographed.
I think this girl is just another flash in the pan wannabe. She's still a nobody and people are already annoyed with her and aware of the fact that she's a joke. Alli is this year's Haylie Duff- another supposed "star" who had to rely on a famous relative to get photographed because she had limited talented and mediocre looks. Haylie went nowhere, which is exactly what I see in store for Alli. She can attach herself to celebs all she wants, but so far we haven't seen any indication of her supposed "talent" and she's not cute enough to get by on looks alone.