Mary Colleen is known for her quirky enthusiasm. She's strong-willed and opinionated; she loves to debate (some say argue), and she's always thinking if she's not outright talking. She's the loudest and most talkative out of a bunch of kids who almost all had to be loud to be heard. Because of all this, she can usually get people to go along with her plans and ideas. This has always been true: when the Septs were about two, 20/20 nicknamed her "the leader of the Septs" because she would be the one pushing her siblings along. Even now it's true that Mary likes to take charge among her sisters and has a knack for directing what's going on, but the Septs themselves would never call her the "leader" anymore, except to tease her when she's trying to make sure things in the family run smoothly (or so she would say; Melissa would say "bossing people around"). She does tend to be the spokesperson for the group if one is necessary, just because she always is ready with something to say.

Mary is also something of a trickster, and she's quick and clever. Her favorite target throughout their childhood has been Melissa, because the two of them (both being outspoken and determined) constantly drove each other crazy. At least it can be said that Mary's tricks are always harmless except to the ego, and they're a better outlet for her great passion than the alternative, which is her temper. If someone really upsets her, they're in for it. Fortunately, Mary has gotten better at controlling her temper: she would rather shine with cheerfulness than tell someone all the carefully considered reasons they're an idiot. In the end, she's a person of great intensity, so it's a good thing it's hard to really get on her bad side. She's very devoted to her friends, her family, and her favorite hobbies and interests, and most of her energy goes to those things.