I agree, the only people that would know she up and decided to leave after planning to stay the night would be the people at the party
I've heard that PP is friends with EA and invited him
Just to go along with the theory for theories sake... What if Christina was fed up with HF's involvement in some of the more dangerous drugs like Molly or w/e, but she didn't really have a problem with something relatively harmless like weed. I'm not judging her for this, but if you look at her SM and know anything about weed, yeah, I'm pretty sure she smoked it. So the friends from Allen want to buy some, she delivers it & will take the money back to HF. People at the party then know she has that money on her.
I'm just hypothesizing for the sake of the theory, this isn't actually my theory.