Gosh, with all the warnings to "be nice" I thought I was going to be asked to watch a disaster. But no! You ride pretty darn well. I know many people commented on your leaning forward and I think you were doing this due to your instructor asking you to use "half seat". If not, then I , too, would say sit back.
Your lower leg was so stedy and it's position very good, and it's place in the stirrup real secure. It looked a bit like you were working a bit hard to keep the horse going, so maybe you need to slow down engough to find her natural rythm. The extra kind of over rolling you were doing with your seat made your hands a bit over active. If you really want to do half seat, maybe you could put your hands down on each side of her wither and let her carry you and you just flow over her and with her. She doesn't need much steering in a situation like this. What a cute, honest mare. Such a confidence booster is a gem.
Mac is like that, but he wont' stay out on a circle without some encouragement with the rein or leg.