Hmm... actually... I think that if my g/f (if I had one... ) threw a ball at me I'd be mad at her for a bit anyway, not smile back (what kind of reaction is that?!?). But people are different, and I don't think anyone who doesn't feel anything for you would even THINK of smiling at you after getting smacked on the back of the head with a ball.

Anyway, that thing about talking a lot and her sharing her problems with you may or may not be good. Either she feels comfortable around you as a lover or she just feels comfortable around you as a friend. So... yeah... be prepared for the worst, but I still think you should give it a shot since the odds are in your favour now! (Actually even if the odds are not in your favour, I still think you should give it a shot. Love is too strong an emotion to keep inside oneself in my opinion)