Why do my parents allow my brother to go out with his friends, but I am not allowed to?

My brother is 11. He always gets to go out with his friends, just as long as there’s a parent watching them. I am 14. I asked her multiple times if I could go to the park with my friends or my boyfriend and she would always say no, then she gets upset at me for not having friends and hanging out with them. Why is she doing this?
Why do my parents allow my brother to go out with his friends, but I am not allowed to?
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