Why would a friend pick at my insecurities?

My good friend always seems to poke at my insecurities, she also one ups me to show how she’s better than me in any area I’m insecure about. For instance, if I’m insecure about my hair, she’ll talk about how beautiful her hair is compared to mine. She also said “I know you’re insecure about certain things.” If she knows they’re my insecurities, why would she always pick at them?
Why would a friend pick at my insecurities?
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