I think we are seeing some of the same things. I agree about the front foot. I'd rather see the pelvis open the foot. The extension stuff you are talking about I suggest would vary with pitch location.Im new to this, but that is a pretty good looking swing. The two things that stuck out to me is #1 right after contact she is not extending fully through the ball and almost slightly rolling her wrists. #2 her front foot is opening up to much to soon.
Look at this clip to compare.
Hitting - What Makes Manny Ramirez Such a Good Hitter? | Softball Performance Blog
You will see that Manny gets full weight transfer, extends all of the way through the zone thus getting full power at contact.