Does she like me or is she being friendly?

Me and her never talked until we got put in the same group. Now that we are in the same group when we are in class we talk a lot. The other two people in our group are quiet so its usually just me and her talking. She punches me on my arm a lot and kicks me when i tease her. Everytime she walks by me she kinda bumps me. She has pinched my cheek a couple of times. I usually don't touch her though because she isn't that kind of girl. But outside of class its like we don't know each other. We never talk or even say hi. When we do its usually her telling me to do something for the group. Usually i would think she liked me but we are so different and from such different cliques that idk. She also told me to add her on facebook to send her this paper when i could easily send it to the school email. What do you think?