I thought I read a study one time that said inbreeding doesn't necessarily lead to physical defects any more than if two people of low quality genes were to mate. I say low quality as birth defects are already in a high percentage of the off spring.
I have a theory that people with good genes tend to be successful people and there for have less exposure to inbreeding.
Anyway, who am I to judge what that lady and her brother had/have. I don't have a sister so I can't directly relate, but I do have some hot second cousins that I would bang. LOL.