Karen Stohlman is one of the best friends of Maryellen Larkin.
Karen has long brown hair and is a ballerina. She likes for everything and everyone to be the same and the three girls (her, Maryellen, and Karen King) to match nearly all of the time. She usually has brand-new clothes, as her only older sibling is an older brother and so new clothes can be purchased for her. Karen considers her brother--and all boys except Davy--to be a pain.
Karen's uncle fought in Italy and was killed in combat in World War II. Because of this, she initially is very rude and insulting to Angela Terlizzi since Angela is from Italy, and says that she could never be friends with an Italian (an example of how Italians were not considered "white" in America for some time).
Karen lives in a different neighborhood than Maryellen but she sees her at school and is in the same Girl Scouts Troop (until Maryellen stops to be part of the Science Club).