Is it worrying that a 13 year old girl has matches in her room and draws naked people?

[Penny]

She's 13, she is a goth. I am worried because I recently found out that she has matches in her room through my younger daughter but she wont admit it. She burns them in her room, I don't know what to do! Also I think she is bisexual and she has nude drawings of women's' bodies in her sketchpad, Problem? also she posted a picture of these on twitter and said she was drunk, she doesn't go out alone and she has no alcohol in her room, lying? she spend all day basically in her room and it is worrying what she is doing in there.she also is swearing on twitter, what to do?
I don't think she actually gets drunk because we never smell or see anything and it is currently the school holidays and doesn't see her friends much and she can't go out alone. there aren't any empty alcohol bottles or anything in her room. maybe she is trying to sound cool online?
she goes to an all girls private school and the only boys she is friends with are those on her coach home from school who never come over and she can't go out alone