My filly used to be stubborn about picking her hooves up, too. First, I would ask by leaning into her shoulder or hip and sliding my hand down to the pastern. When she didn't, I would leaning with more weight into her. Still no response? Sometimes twisting or pinching the chestnut will get a horse to lift their hoof quickly.
I trained her to lift her leg by saying "Up" and holding the pastern of the leg I want her to lift. It took about a week, but it was well worth the work. I would twist or pinch the chestnut, while saying "Up" if she didn't lift it when I leaning into her and said "Up". Gradually, you become less physical when asking, because the horse is learning that "Up" means to lift the leg.
Hope this helped! :)
Jessica Fox & Shez Kinda Impressive
2009 APHA World Top Five SPB Longe Line
2009 ICPHA High Point Yearling Longe Line.