Why did a girl who liked me acted so shy around me and now when she likes someone she acts absolutely different?

There was one girl who liked me. She liked me from what i heard already one year before we became friends and met. But i would never say she liked me. She never said anything first and if i wouldn’t say hi first she wouldn’t say it. Her friends always talked to me more and she was kind of like just there and didn't talk much. I found out late that she liked me. But now when she likes someone she is different person. She is loud around that person, she is teasing and flirting. I dont get why she was so different with me. Not saying she should make a first move or anything but i just dont try with a girl who doesn’t show any interest.

Why did a girl who liked me acted so shy around me and now when she likes someone she acts absolutely different?
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