Have you tried her in cloud boots? So many of these navicular horses are becoming sound again now with correct barefoot rehab, but it’s VERY particular and they HAVE to get comfortable enough to have a distinct heal first landing which the cloud boots help with as they have therapeutic wedge pads. The trimmers who specialize in barefoot rehab for navicular rehab generally recommend them for a period after pulling shoes to strengthen the digital cushion and therefore the entire caudal aspect of the foot. I went down this road last year after my 4 year old was diagnosed.
Look into the research of Dr. Robert Bowker, Rockley Rehab, Daisy Haven Farm and the Progressive Hoofcare Practitioners. The Humble Hoof podcast is amazing too. I know sound like one of the “crazy barefoot people” now, but hopeful for you that maybe your horse could come out of retirement one day😊