She gets tongue tied around me. Why?

There's this girl, I kinda hinted that I like her. She's really quiet in class but has a lot of friends outside of school.

the first few days, she was like smiling coyly at me, happy looking and her friends would stare at me.

after a week, she's kinda walking fast away from me, wouldn't walk near me like I'm some kind of cancer.

and when I say Hi, she gets tongue tied like she can't say hi back, biting lips and looks tense, looks away quickly...etc

thanks.
She gets tongue tied around me. Why?
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