Dimensions of Karina's Asymmetry

I've watched Marijke's videos where she works with some other people's horses and it seems to me that she is moving with the basic ST exercises quite fast. Sometimes she starts to work on shoulder-in on the very first day. On the other hand, I've seen her work with some extremely crooked horses veeery slowly, even slower than I work with Karina. And now I'm not sure whether Karina's way of moving justifies my extreme caution. In fact she is sometimes able to move with her head forward-down in trot and canter even, she doesn't put too much weight on her front legs, she is able to engage her haunches and free the shoulders - a little, of course, but the improvement may come in time. What worries me actually, is that there exists some visible stiffnes in one of the hind legs and that Karina is diagonally imbalanced. Her left front leg is also more developed, her left shoulder is much bigger than the right one. There are problems with the lateral bend, because on the longe she often moves to the left and is bent to the right, with her right side muscles tense and hollow and she should be moving with her righ side long and round. I have worked with her on long reins, but that doesn't work exactly as I wished, because when the outside rein is behind her haunches, she keeps on hurting her mouth with every step. But when the outside rein is thrown across her back it really works fine and prevents her from falling out through her outside shoulder. But then it doesn't prevent the hips from falling out, and even the wall of the roundpen is not enough. Before I bought Karina, she in fact has never worked on the longe properly, and she never walked on the longe to the right at all. The former owner told me that she didn't want to go to the right, so he never forced her to. But she soon learned that she can move to the right also (I didn't force her, too - I just asked a few steps at first, then one circle, then another and another), though there are still problems with the bending and so on, but I don't expect them to magically disappear after so many long years that causing them took. It is wonderful that I finally found in the meanders of the Internet materials, which explained to me so much and helped me to name and define the problem. Because how could I work on a problem if I didn't know what it actually was?