I have this very same problem with my daughter. She is herself shy, careing, compassionate and thoughtful and she isn't into girly stuff like shopping and hair styles or music. So she has TBH only one good friend and three others that she says are friends but just let her tag along.
The one friend she has is often mean to her but daughter is so soft she lets her get away with it.
We talked about how this friend seems mean but in reality she is just finding seniors difficult to navigate. She is so comfortable with my daughter that she knows she can, to a degree like family, take out her frustrations with the girls she wants to be with but don't want her around on her.
I have advised her to talk to the girl when she is being mean. Even if it is just look at her and say no that's not nice. And to see how that goes. They have been getting on a bit better just now but girls of a curtain age are fickle to say the least. If your friend (or my daughters) is allowed to be mean they will get into that mindset forever. Best to nip it in the bud if you can.
Have you any other friends you can spend more time with?