What does she mean by doing this?

We know each other since 4 years since when I was 9 years old and now I'm 13 and crushing on another girl and I also see her with some other guy. I have liked her from the day I saw her for the first time then but didn't know she had crush on me too until my friend who I got reunited with after very long time told me she used to like me before when we were 9. When I was 9 she used to smile at me and even initiated a conversation one time. My elder brother use to joke about me marrying her in front of her but I don't remember her reaction to it. Now she doesn't talk with me but all of my friends and wouldn't even look at me. And recently when I was talking with my friends she and her friend from distance were laughing at me and said this "I should run away before he has a crush on me" and ran away laughing.
Why did she do this? What does it mean?
What does she mean by doing this?
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