From my recent experience, I'd probably delete her if it's causing you pain. I'm friends with all sorts of exes on FB, but I don't have any feelings about them either way..they all have girlfriends now or wives that I know and like. But, this kind of think can stir things up if anything is remotely unresolved. Not having a daily reminder will make it easier to move on (whether that means getting back together eventually or finding someone new)....