Thank you for your help, Katie! I had reviewed that post as well. Based on it saying "inwardly rotate the lifted leg" I believe the hips should stay square and not open up.
I love this pose but it challenges me both physically and mentally which is why I chose to work on it. I do believe abs have something to do with it. I also think it may be the butt and lower back? I could be way off here. I'll keep working at it!