Many reasons for thin soles, most of them purely mechanical. Her heels were very high with the original rads from a few months ago. Suspect she's been trimmed 'status quo' with that form for quite some time. Somewhere along the way folks are told that ponies have tin can feet so they have high heels...or someone in their care, farrier, owner, trainer, etc, thinks a horse needs highish heels to stand on.
So it will take time for the sole to develop more thickness. It grows at a snail's pace under best of circumstances, much less having to heal the damaged corium under the front of the CB that was impaling itself onto that corium until recently, reorganize and then start producing horn again.
Protection of the sole of the foot is imperative. There is nothing in the anatomy of the foot to support/protect the sole in the front of the foot Whether you use boots/pads, foam taped on, maybe a composite with some tweaking of the trim, whatever works for you best.
EC Primary Response