SPOILERS for Dollface by Lindy Ryan

This post contains spoilers; proceed with caution. 

Darla, the neighbor, killed the barista and injured the other PTA members. She was crazy. But it was Jill's sister, Kitty, who killed the others at the Halloween Party. She was jealous that he sister had found new friends and was distracted by the attacks. Kitty was also the one who killed Jill's bird when they were kids.