Honestly, the likelihood of a 13-year-old staying alive, never mind pregnant, after a gang-rape, with the kind of healthcare available in Westeros, seems rather small to me. It's extremely likely that she would have caught an infection that would have taken her fertility if not her life. Some time ago someone post a link of a very relevant interview with an OB/gyn who treats gang-raped girls in Congo. He said he couldn't save most of them, particularly when they were very young, and most of those he did save remained incontinent for the rest of their lives. I know GRRM likes to think that no one ever dies of a gang rape, but I don't think a woman could work as a whore if she was incontinent. I agree with Gerion as the Sailor's Wife's husband.