How do I ask a girl out who I have been friends with for years?

This girl lives in my village and her family are friends with my family. We used to go to the same school but now we don't and she is in the year above me, so I don't know much about her friends. When we are at each others houses and watching a movie we sort of snuggle up together even when there's room on the sofa, and I have been and am going on a summer holiday with her family. You may say that I should just ask her out but I don't know if she acts the sane way with me as she does with other boys at her school. Please help and thanks for any comments. Btw I'm 14 and she's 15.