Mary Carmichael hates men. She tells you so herself:
MARY: I hate men. I loathe them. If one of them so much as touches me, I want to sink my teeth into his hands and bite it off.
Mary's at Green Manors because she's mentally ill—and the illness takes the form of a pathological hatred of men. She needs to learn to like men to get better.
As it happens, that parallels the problem of her psychiatrist, Constance Petersen. Mary's flirtatious while Constance is cold, and Mary's outright ill while Constance is just repressed.
Nonetheless, they're both portrayed as out of whack… because they aren't fond enough of guys. In a Hollywood film, women are supposed to like men and go off and get married. If they don't, you send them to an analyst before they hurt someone.
Carmichael, incidentally, is played by Rhonda Fleming, who went on to become one of the most glamorous Hollywood actresses of the 1950s. The scene with Mary and Constance, then, is a kind of a nightmare-vision: what if all these incredibly beautiful Hollywood actresses like Ingrid Bergman and Rhonda Fleming suddenly decided they hated men? What, oh what, would Hollywood do?
Luckily, Mary's whooshed off screen quickly, and Gregory Peck shows up to make sure Constance isn't frigid. Men everywhere are saved—just barely.