I really need to stop even opening winsister fics, no matter how much I'd like a crossover between spn and another series I like. It pulls me out of the story every single time the char's name is mentioned and stops me from even starting to enjoy anything else halfway decent about the story.
I don't even hate all oc's, but adding a sister to the Winchester family rarely if ever, pretty much never in my opinion works out well. The rare few cases that it does work, it's a half sister whom they don't meet until after they're full grown, a la Adam.
But adding a sister who grew up with them, who's a daughter of Mary and whom Dean cares as much about as he does about Sam, esp. as in many stories, she's younger than Sam, just makes me lose all interest before I've even gotten through one alinea with the oc's name in it.