I don’t know what to do

My 9 year old niece has hair on her arms and legs, and one of her friends said something to her about it. Now she doesn’t want to wear shorts, skirts or dresses. She wears her sweatshirt to school everyday and leggings. My sister won’t let her shave yet, which I don’t think she needs to anyways. Everybody has been trying to help her understand that it’s okay for girls to have hair on their body, and if it wasn’t it wouldn’t grow. I plan on getting her some books on puberty, and going to get her some clothes she feels comfortable in (maybe some maxi skirts and long dresses.) Does anybody else have any ideas on what to do, because she’s stubborn, and I hate that she feels ashamed of her body? This isn’t the first time one of her “friends” has made fun of her either, and she has such bad anxiety and low self esteem that she just believes everything they say to her. Any suggestions would be greatly appreciated!