Why does a girl have pictures of me on her phone?

I don't really know this guy extremely well but I've been getting signs that she does like me. I asked whether to could hangout and she said no but nicely (basically a rejection). I was talking to her on a bit and when she was looking in her gallery I saw a collage with my name a pictures of me. She seemed to panic a bit but then I looked away without noticing. She never seems to want to talk to me often and either stares when I don't notice. She's also always one of the first to look at my Instagram stories.
Why does a girl have pictures of me on her phone?
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