Why does a girl who doesn't know me light up when she sees me everytime?

I've noticed there seems to be some kind of connection between us. Like she is treating me like she knows me. For example I'm noticing she is waving and smiling at me. She is making effort to do that with me. Her eyes are also widening when she sees me.
Why does a girl who doesn't know me light up when she sees me everytime?
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