I second what Imagine said...I NEVER immediately ask for 'foward' movement. Get her bending, sideways, ask her to move her hips one way and the other, teach her to yield her shoulders...basically you are going to help her unstick her feet without ever actually 'asking her to walk foward' in the traditional way. I also use a rope halter.
You could also always use the old standby "butt rope" to help her figure out what you are asking for as well, but make sure it is separate from your lead that's on the halter.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."