Paulina is Shamrayev's wife and Masha's mom. She's having an affair with Dorn. Just as Sorin serves as a cautionary tale for Konstantin, Paulina should be one for Masha.
She's trapped in a loveless marriage and in love with someone who doesn't love her back. In Paulina we see that the young people don't hold the monopoly on folly in love. Faced with Dorn's indifference, she presses him to take her away, stop seeing other women, and change her life. He responds with a resounding "meh", "I'm fifty-five. That's a little late for a change of life" (2.68).
She's extremely jealous. When Nina gives Dorn flowers—an innocent gesture—a furious Paulina tears them up and throws them on the ground. Like her mistress Arkadina, Paulina is histrionic and manipulative—she's just less effective at getting her way with these qualities.