Why is this girl eavesdropping into my conversations?

Like lets say I'm talking to my friends and she is in the proximity but I'm not talking to her, obviously, and she either laughs at something I say or makes a comment or a sarcastic remark or if it is some sort of complaint she will make this crying sound, like if I'm being too dramatic. Of course, if I talk TO her, she acts like if I'm the least interesting and unfunniest person in the world and yet things that are none of her business she finds fascinating.
Why is this girl eavesdropping into my conversations?
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