Why is she acting like she is avoiding me or pretending i'm not there?

I'm not sure what is going on. She is acting overly quiet towards me for no reason. I really like her, but what is weird is I sit next to her and she ends up showing me her nice pen she has got. For some reason she gives me this small chat which she starts. Then she goes quiet like I don't exist. We've spoken before and I've only been nice to her, but I have noticed she will talk to others normally but not me.

Why is she acting like she is avoiding me or pretending i'm not there?
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