I agree with David that (1) Yes, it is possible to dance in a partnership of considerable height difference, and (2) It does create special circumstances that make it more difficult. Not impossible, but difficult. Flaws in technique are more obvious, so you have to be twice as perfect as everone else.
However, I don't agree that reaching is the skill your lady needs to improve in order to dance with you. No matter how much she reaches her leg out of your way, her body will still be in your way unless she moves it. This is the job of the standing leg.
In all likelihood, she will need to work on keeping her center picked up as she moves back through strong support from the front leg. She'll also need to work on continuing the movement of the center back past mid-stride, without dropping, through the controlled and gradual lowering of the back heel and leg. If her center drops at the beginning of the walk, you'll find that your leg has nowhere to go. If it drops after mid-stride, you'll have trouble with your knee bumping into (forgive my bluntness)
her crotch.
I don't mean to sound discouraging, but the truth is, you will need to work a little bit harder than everyone else. The good news is, you'll both be better dancers as a result.
Sincerely,
Jonathan Atkinson