How can I tell if she's stalking me?

I met her about two weeks ago, and for the first week, we got along really well. This week, I've been running into her every day in unlikely circumstances, and this last time, she was facing the entrance to the store I went into, and gave me this big smile, that I might just be imagining this about, but it seemed like the creepiest thing I've ever seen, and then when I checked out she just kind of lingered by the counter. I don't have enough events to know for certain, and there definitely isn't any proof, plus the fact that I'm a large man and she's about three quarters of my height, which isn't at all what you expect of stalking, but I just get a creepy vibe whenever I run into her outside of class, and the number of times we've run into each other is very unlikely, so I just don't know. How can I tell for sure?