I would highly recommend reading the book “Queen Bees and Wannabes.” It’s written by Rosalind Wiseman. It’s really written to a target audience of parents who have daughters in elementary, junior high, and high school. But an awful lot of the stuff in that book does happen between adult women. It has some very helpful suggestions in how to deal with passive-aggressive females.
If you don’t want them to see you reading it, purchase it as an e-book and read it on your phone, tablet, or computer.