Your sister, your only sister. She is your sister but a friend and the most amazing one at that.
First slurred out when I was drunk because there was no one word invented for her yet.
Sisterfriend is the best of both worlds: First she is your blood- Second she is your friend-confidant-reality check. Sometimes you fight and sometimes you get ridiculous with each other. She is a friend that will always be there because she has to- she's your sister duh!!!
I heart my sisterfriend so much but I'll slap that bitch if she borrows my clothes without asking again.