I reread that part. This is just yet another example of the adaptation not giving a shit. In the light novel, Lessy is on his side, and Myne stands up, with her upper body half outside the window since Lessy is only half as wide as she is tall. That’s when she gets grabbed by the light rope and is pulled out of the window. The size of Lessy is the same in the anime, so there was absolutely nothing holding the adaptation back from doing the same here. But instead, they opted to have her climb out of the safety of Lessy like some idiot. At least they are consistent, since they prove in every single episode that they neither read the source material nor understood it.