She could just be thinking.
Sometimes people are so focused on their thoughts they don’t notice where their eyes are directed at. It can appear they are looking at a particular body part, but in reality they are not consciously focused on that part and analyzing its details. It’s like being in deep thought and looking into the distance but not acknowledging what you see.
Direct and clear verbal communication should help resolve this behavior. I know its tiring, but the effort is worth it.