"instead of 456 close, we are doing a 4 5 &6, Chasse' HOW do I lead it so that the lady does not close and slows her rise?"
Well first you have to recognize that you do both close your feet in a chasse, you simply don't finish there - you seperate them into another step, and it is on that step which you lower.
So, dance a bit flatter yourself so that the rise is more gradual. As your feet close and you change weight, push out and very slightly up from your new foot to project your bodies into that extra step. You are trying to make the foot closure feel like it doesn't give a sense of "closure" to the accomplishment of the figure, but is instead a temporary place on the way to something more - which would be moving into the seperating and lowering step which does end the figure.
Don't worry so much about leading it, worry instead about dancing it clearly yourself, then she will be able to follow the difference in how you do the chasse vs how you do the other thing.