Why is a girl avoiding me for no apparent reason?

She is acting very quiet with me and only me. However, tonight she fell off her bike and I was driving behind her. I stopped to help her and to make sure she was ok talking heaps to me and laughing, and she did say she appreciated that I had stopped for her. I do really like this girl. She just seems quiet with me for some reason. I've always been nice to her

Why is a girl avoiding me for no apparent reason?
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