I don't think there was any special way she developed her skills. They've been married for over 50 years and my sister in-law can judge just by watching and listening when my brother is hearing. Watching my brother's face I think was part of it....she can tell quite accurately by glance whether he is hearing conversation. And of course, just by his response or lack of response! He has always been an engaging person, so if he is quiet, it is indictive that he isn't hearing well those who are speaking.