I think Mia has the right answer, but I feel uncomfortable adding that many details to their answer, so I'm posting my own. This indeed matches Diane Hoh's The Invitation.
At the party of the year, a rich girl’s practical joke turns deadly
For the high schoolers of Greenhaven, Cass Rockham’s fall party is the social event of the year. Each October, students wait by their mailboxes, praying for the gilt-edged invitation that grants entry into the inner circle of the most popular crowd. And now Cass has planned her finest party yet, with a new sauna, a hot band, and no parents for miles. But to make this party really killer, Cass tops it all off with a sinister twist. Nerdy Sarah Drew is shocked when she and her friends receive invitations to Cass’s affair. For years she’s steered clear of the popular kids, and now they want her to come to their party? Sarah is wary, but her friends talk her into coming with them. But she regrets it quickly, for at Cass Rockham’s mansion, the only party favor is death.
From the Google Books excerpt:
Breathing a sigh of relief, Ellie bent to pick up her dress.
And screamed in horror.
There, settled on the bodice, smack in the center where it couldn't be missed, like some repulsive, fat insect, was a huge, bright, purple blob of nail polish.
She indeed blames her sister, Ruth, and then borrows a dress from her mother.
As far as I can tell from reviews of the book (1, 2), there's nothing supernatural, just a spree killer knocking them off in a deadly scavenger hunt.