I'm about to say something I've never said before. But a horse who intentionally strikes out is a serious offense. I would carry a crop in my boot, practice teaching her the typical yielding skills without anything besides your halter. I prefer to teach my horses in a flat halter as they're going to live their life in a flat halter so they might as well learn to respect it right away.
I also strongly believe that a horse will respond to whatever it's trained to respond to no matter how mild or how strong. Rope halters are good to use when you're handling her until she's better trained, but I'd personally work on getting her respectful in a flat one.
So... practice teaching her to yield her everything to you. ANY acts of disrespect at all - if a single foot comes off the ground uninvited aimed in your direction should be met with a quick hard slap on the offending limb with the crop. She will probably be stunned and jump - but that's ok. If you were momma-mare in her herd and she just struck out at you she'd get her butt kicked worse than your crop can do. Her striking out at you when you ask her to move is simply her saying 'no i dun-wannnnaaaa' She's in charge. That needs to change fast and furious.
That being said I would go back to all that ground work I mentioned in my first post. All of those skills are what asserts you as 'in charge' in your relationship, the more you do that the more she'll see you as the 'big momma' of the herd. Belgians, whil I love them to death, are pretty fiesty for draft horses, don't give in :P Still happy to hear you're getting help :)