That is why I am hoping the comparison clip I posted will help. Believe it or not most of our work and foundation is rotational forces BUT that big dip and flex of the back knee almost requires a linear push so that will hopefully be a concept she can grasp. I am pretty sure her bat speed and plane will improve if she can make some incremental changes as you suggest.I think to get her to understand and feel it like we have been talking about think rotational versus linear....as discussed both are required it's not an either or but she needs to be less linear which gives her the slide back and forth look and feel and more rotational which should give her a coil and uncoil/release look and feel. We can discuss tons of little mechanical issues inside this but as a cue I think it might work the rotational would involve loading with more coil and then staying back more and releasing sooner before the drift forward.
Again we are tinkering with a very solid foundation and you don't want her to lose form on everything else she is doing so make incremental changes. Maybe even have her discuss video breakdown with her coach and see what they think although if she is already experiencing success they might just go with the don't mess with something that is working and honsetly I wouldn't blame them.