I don't think that it would be a problem to list your SiL. People talk about me as their attorney all the time even though it's *just* because they are related to me. In this case, your SiL is giving you some medical advice, though she's not the treating physician in all respects. They may want to request any medical records that she would have on you, but if she doesn't have them to send, she won't send them. :)