I can sympathize being more comfortable riding on my tie side as well. Sounds like she is just afraid of picking up speed and is leaning back. She'll need to get over this fear and put her weight over her front foot. She'll have more control this way. It will come with time as she gets more confident with handling speed.
I'm not quite sure what you're asking regarding her stance. Are you unsure of whether or not she rides regular (left foot forward) or goofy (right foot forward)? If so, the test that makes the most sense to me is have her slide across a hardwood/tile floor with her socks on. The way she faces when sliding with her sock should be the way she rides on a snowboard.