My 13 year old daughter only talks to her older brother?

[Joan]

Okay I know for a FACT it's nothing sexual. She has always looked up to him ever since she was about 2. He's 23, they have always been really close. He dropped out of school his senior year,he still lives with us he smokes and cusses pretty bad, but that's not what worries me.She will only talk to him, hardly ever to anyone else unless they ask her a question then she will quietly answer. She's so shy at school she doesn't have any friends and another part of that reason is she's kind of small,skinny,and quiet,plus she's a late bloomer so they pick on her sometimes.I'm not even exaggerating all she does is come home do her homework and follow him around and talk to him, and when he's in the shower or in the bathroom she quietly watches TV with her younger brother and sister, but the only time she talks to them is when they talk to her and barely talks then.She has always been so shy, but never this shy it's been going on for about 2 years. I have no idea what to do.I don't even know her favorite color! I'm sure he knows everything. I love them being close, I think it's sweet but I want her to break out of her shell and have friends at school. I just don't know how to talk to her.What should I do?