Milly has short curly brown hair, blue eyes with a dimple, freckles, and a yellow bow (not always completely visible), and her uniform has a red collar, red circular pattern on the sleeves and the bottom, white socks, and black Mary Janes.
When Milly turns her head, her bow and dimple switch places. This means she's an ambidextrous sprite. Sometimes, her bow stays in its current place, but the eye twitch always switches.
She is also the only Fireside Girl that is playable in Game Smash.
According to her statement in "Isabella and the Temple of Sap", she has 53 Help Thy Neighbor Patches, because she went back one afternoon when everyone else went home. This has yet to be seen in an episode.
Before Melissa's appearance in "We Call it Maze", she was the only Fireside Girl with black shoes; the others have red shoes, varying a little bit in appearance.