The story was a bit jumpy and could do with proofreading, but I loved this. It was so adorable and it holds a great message :) reminds me of me and my friend. I never had a brother or sister, so she's like my little sister and we've always been like that. She beat up a guy for me once.
But yeah, this was awesome and you have great potential with your writing style, like the first couple of lines were absolutely amazing. It just jumped a little after that :)