Contra >>2, I don't think it's that odd for someone who just thinks of you as a friend to spend that much time with you. I've had close female friends where that wouldn't be at all unusual.
However: it is an awfully long time to spend with someone you just met. So, yeah, I think she's at least playing around with the idea of being interested in you. I think you're handling it right - assuming you're interested in her. (I may be borderline flirting with someone at the moment who I think is exceptionally cool but I'm not really interested in. My conscious keeps telling me to be careful.)
Anyway, good luck, and keep us posted!