Is a girl joking about dating me?

While we are at the BBQ party. This girl I knew she started asking questions like "Do you have a girl friend" I answered no. Later she asked me that if I'm okay with her to be my girlfriend. I just lift my shoulders up like I don't really care in between" sure why not." Later her face expression changed and she said that she was joking. Later she told me that she needs to get some air... Does she really like me or was she joking? I need to know this because we knew each other for quite a few years and I sort of like her.