I need help with this girl?

I'm in 8th grade first of all. I'm not super popular but I'm pretty popular. I sit beside this one girl i like in of my cles. Like one day she was really nice and pretty talkative and the next day she was sort of mean. When she sits beside me she faces her body towards mine. I catch her glancing at sometimes and she does the thing where she looks at me then swoops her head to look at something else then when im not looking looks back at me. She crosses her legs sometimes and her foot is bouncing up and down. i put my leg near the end of my desk and moved it closer to hers and she moved hers closer and kept it there until i moved it. She is also very very talkative and outspoken but when around me she is really quiet. Im also shy too. she is dating someone too