She flirts with me one day, ignores me the next?

I've only talked to this girl a couple times, but the second time I talked to her, she tried to get my attention as I walked by and then when I talked to her, she hit me on the arm a couple times during the conversation. I asked for and eventually received her number (not sure if this was the way to go but I'm still figuring it out). Anyway, I see her once a week, so the next week, something strange happened. When I was about to open the door to the room, she came out of the other side; she just looked at me and I looked at her, no hey or anything, and I just kept walking. Then for the rest of that day she sat and talked with her other friends and we didn't talk or anything. Did I read too much into her before? If I did, whatever, I'm still trying to figure this out.
She flirts with me one day, ignores me the next?
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