How do I know if she likes me?

I like a virgo girl for a very long time, but i don't know if she's just playing around with me or interested in me. I know she's friendly to everyone. When I'm alone with her, she very shy and not talktive unless I say something first. everytime I give her a gift, she's very happy. However, sometimes when I can her, she won't answer my calls and if call too often on the same day, she will just tell me let's just be friends. Then the next day, she will be super nice to me... then she won't be that nice to be later.. after a while she will be nice to me agin.... any thoughts on that? I have no idea. thanks