Perhaps you could attach pics & elaborate? I understood 'sheared heels' to mean they were *perceived* to be too short. But after looking at the above link(& disagreeing with the approach), I looked at the definition; http://ezinearticles.com/?Horseshoei...isks&id=511283
This is also known as 'underrun' 'collapsed' or 'crushed' heels.
I don't get what you mean 'recently...a bad bout', as this is generally a long term prob, but assume it has been going on a while, possibly unnoticed, until it recently made her lame?
My perception of 'boxy' feet(unless this just means high heeled) would also give me the idea these feet are less 'predisposed' than say, flat, flared TB type feet. IME back feet are also much less likely than fronts to become underrun. Tho the basic initial cause is much the same in either. The walls have been allowed to overgrow. If the walls are allowed to become substantially longer than sole level, forcing the walls to bear the weight, Toes tend to become stretched forward, pulling overlong heels forward too.
Keeping the feet *well* trimmed and ensuring lots of exercise are 2 major factors in healthy, sound feet. Pete Ramey hoof care heals founder in horse’s navicular disease farrier
will give you some more food for thought.