Girls what does this mean?

What does it mean if you are walking towards a girl in the halls you make eye contact and after a few seconds she smiles first at you? Could it just be to avoid any awkwardness of the situation or could she possibly like me? Also we are seniors in high school and she is shy. Also this has happened multiple times and when I said hi to her once outside of school she gave a big smile and sounded really excited but then she ended the conversation rather quickly.