Hers probably didn't break off because she was in a small pen where she couldn't move much and she was in deep crap and mud.
Soft ground and not moving, and she's not heavy like a horse, and they don't wear like they should.
The horses I saw had shoes on, that kept their feet from wearing, and they went straight out in front like skis, as long as the rear hoof on that pony. Same thing... small pen, muddy soft ground, and shoes.
From Hair's keyboard to my monitor:') I think you are right. Normally, they should have broken off. Didn't the girl also say, she walked by and saw her?