I had the same problem at first. What I did was take a rope and put it around her foot and lifted her hoof up. (Like you are going to pick it out with a hoof pick) and held the treat under her chest. At first I gave her treats for just trying, then I actually made her go down and she didn't get the treat unless she did. Eventually they'll do it without a rope, and then you can start using a command instead of treats to do it. And always wear a helmet, just in case they lose their balance or something.
If you ever do bows with any of your horses, I'd love to see more pics.