What is this thing in my Cat's skin and why is she acting weird?

Hi, I'm Julia and I have an 11 month old kitty named Luna. She has this thing on her leg-hip and it's like coming from inside of her and it's hard and stick shaped, and it feels like a bone, or some infection from a bite (A neighborhood cat named Brother bit her) and at first she didn't seem like it hurt, unless you touched it. Luna is a very energetic, sweet, outdoor kitty that we rescued as a sick stray when she was three months old. She has been so tired, and sleepy, and it's not normal at all and she's been hiding under the bed which isn't normal either, and nobody knows if she's even been eating or drinking because no one was home. And then a friend, this little girl Niki, dragged luna out from under the bed and held her, but Luna didn't like the way Niki was holding her, and so she squirmed, and meowed, and so Niki dropped Luna and Luna fell on her back with a thud. And she tried to meow but no sound came out and Luna looked so shocked, and she got up and limped away, limping, back to under the bed. I'm so worried about Luna, even though I'm probably overreacting, I love her so much. Thank you.