K.M.
I am a shy person and can tell you that what most people see as us being stuck-up, mean, aloof etc is simply us being shy. It doesn't mean she doesn't like you. Because she is shy it takes more to bring her out of her shell, we tend to like one on one situations and it takes us longer to feel comfortable in larger settings. So now living in a house full of people she may be a little uncomfortable, not because she doesn't like anyone. Everyone else in the house has bonded on a different level than she has, now she has to come in and try to find her place, that's hard for anyone especially a shy child.
I like lynn's suggestion. You may have to be the one to start things for awhile. Also take her out just the two of you, so you each can get to know each other, take her out with just you and the girls for a spa day etc. It makes for a more relaxed environment and helps her to feel more at ease. She will come out of her shell then.
Good Luck.