Ivy's a tough one to gauge. On one hand she likes to have fun. Also, she has no qualms about doing anything necessary to advance her goals. On the other, she has a low BS tolerance and, especially after Axel, doesn't like being manipulated.
As long as Ivy believes Billy will benefit her, she'll be all in. If she suspects the whole thing is is scam, however, her reaction becomes harder to predict. I can see her basically deciding, screw it, and enjoying the party for the weekend before telling everyone to screw themselves when the party is over. I can also see her being the first one out the door if she really believes they are trying to use her. Likely it will be different outcomes based on choices.