One of the headmistresses and founders of the school, Karen is “an attractive woman of twenty-eight, casually pleasant in manner without sacrifice of warmth or dignity” (9–10). She has been best friends with Martha since college and is engaged to Dr. Joe Cardin. Karen is reasonable and well-liked by all of her students other than Mary Tilford. She tries to reach Mary, offering a safe place for Mary to talk when she feels like she cannot go to class, but Mary remains closed off. Karen is patient and fair with the girls, which make Mary’s claims of unfair punishment seem even more ridiculous. Karen is intelligent and easily sees through Mary’s lies. She remains calm at times when Martha gets upset, especially when dealing with the children.

Karen is also strong and sticks to her principles, even to the point of stubbornness. In the third act, she has the option to save herself and Martha by marrying Joe and moving to Vienna, but she sabotages this chance. Joe admits that moving back and taking his old job in Vienna is a step backward and not what he wants. He is trying to rescue Karen, and Martha with her, but she will not let him sacrifice himself.