Hmm. There is no "official" way to take off bell boots. You'll just have to teach your horse to stand. First of all, when you lift a hoof to pick it out, use the chestnut for the front hoofs and the cap of the hock for the back hoofs, instead of pulling up on the fetlock. Next, rub your horse's legs everywhere except for the chestnut or cap of hock. If she lifts her hoof, keep rubbing until she puts the hoof down. If she leaves it down for awhile, reward her by going to her shoulder and rubbing her. Keep rubbing her leg (this may take a few days) and only using the chestnut and cap of hock to pick up the hoofs, and she'll soon understand that she doesn't need to pick up her hoof unless you touch her chestnut or the cap of her hock. No horse wants to work, so she'll soon figure this out. I have a mare that lifted her back hoofs and kicked every time you touched her back legs. I rubbed her legs well twice a day when I fed her, and used the cap of her hock to lift the hoof. Now, I can rub her hind legs and do stuff around them without her lifting them.
Hope this helps!