What about EZ boots all around? Wouldnt that get rid of the mud issue and protect the feet from further chipping. They can be removed for cleaning and medicating. This would be the obvious option to me, but maybe I'm missing an important detail in why they won't work. Even if she wont hold her feet up for long if you can start to get them on and she puts her foot down you can probably finish the job. Don't be afraid to handle her feet either, to many people think that their horse is just impossible to pick out because they are afraid of being stepped on or just general fear of the damage a hoof can cause. Be deliberate and end on success, she will figure it out.
Troubled TB ~"A thorn by any other name will prick just as deep." @-'--,---