I know you said she's hard to lunge far out, but if you're going to lunge her, I'd really try to. I know my guy has trouble the bigger the circle I start to walk because he's trying to figure out where to be to keep the rope tight instead of just moving forward. If you try to just pivot in the same spot and move a max of 1 foot in either direction, does she lunge any better? /I only watched the first video.
Edit: Have you checked her back right leg in particular? That one seemed like it was hesitating a little bit to me in the second video, but maybe I wasn't paying attention enough.