Door from Neverwhere! I used Michelle Trachtenberg as reference. And yes, she's sort of a bum, but not exactly. Her name is Door because she can open any door, locked or not, except one which she can only open with a key.
The book's description:
She was dressed in a variety of clothes thrown over each other: odd clothes, dirty velvets, muddy lace, rips and holes through which other layers and styles could be seen. She looked, Richard thought, as if she'd done a midnight raid on the History of Fashion section of the Victoria and Albert Museum, and was still wearing everything she'd taken. Her short hair was filthy, but looked like it might have been a dark reddish color under the dirt.
Her cheek was grazed, and her dirty reddish hair was tangled; tangled, but not matted. And her eyes...Richard realized that he could not tell what color her eyes were. They were not blue, or green, or brown, or gray; they reminded him of fire opals: there were burning greens and blues, and even reds and yellows that vanished and glinted as she moved.
It occurred to then that her skin was very white, now that some of the dirt and blood had been removed. He wondered if she were pale from illness, or from loss of blood, or if she simply didn't get out much, or was anemic.
Her hair, when washed, was a dark shade of auburn, with copper and bronze highlights. Richard wondered how old she was: fifteen? Sixteen? Older? He still couldn't tell.
She looked up at him, her elfin face pale in the pre-dawn light.
He looked at her then: a small creature with huge eyes staring at him urgently from a heart-shaped pale face.
Door folded her arms and stood taller, putting her head back, raising her pointed chin. She looked less like a ragged street pixie...