Charlotte is a gray mouse who is slightly larger than normal mice. Charlotte wears a white-laced cap with a red bow, which is available as a collector's item in the shop. This cap can either be a mop-cap, a sleeping bonnet, or both, giving her look two interpretations that make equal sense. She complements this hat item with red pajamas with thin, vertical white stripes and white buttons. The fabric of this nighttime apparel seems to be something along the lines of silk, lace, or satin because of the puffy/arid and wavy look of the bottom and body of the nightgown. Upon waking up, she has groggy eyes, a sign of her exhaustion from waking up for such a long period of time.
Obviously, Charlotte is a very heavy sleeper. She is able to sleep for four months without waking up. This gave her the title of "sleepiest mouse in Transformice," a name that she continues to live up to. Charlotte is also able to take slow, deep breaths when sleeping, versus normal mice who breathe at a moderate rate when using the sleep emote.
It is noticeable that Charlotte has a large array of trinkets in her tree stump. Because of all these items, it is obvious that Charlotte is a collector of past event items and possibly a thief of museum items, unless they are miniature souvenirs. Although not in-game, she owns a fully-clothed penguin plush, evident by the new items advertisement with it laying at the side of her nightstand. She also has featherlike hangings that fall under a single colored bead in the first floor of her stump. These are also not in-game but rather on the announcement image with her trinkets shown.