I love my friend, but I think she is hetero

i started a new friendship with a girl that I love a lot, I had never told her that I like her as I do, cuz im afraid to get a bad reaction, but I wonder if she is a pure hetero? cuz one night, we slept together, I played in her hair, I touched her tightly, then suddenly she hold me so strang, and her heart was beating so fast, I wanted to kiss her, but I couldnt, cuz there were 2 friends of us :s but after this night, she behave as nothing happened. so , can she be bi?

Girls your age are huggy by nature so it's hard to judge from that. Tell her you saw a photo of two girls kissing and ask her if she could kiss another girl. If she says "Yuk" there's your answer. If she says maybe, follow up with, "How about me?" :-)