That’s really not that bad. Gross? Absolutely. But I can tolerate gross sensations. The grossest of which you didn’t hit on. The sharp, pebbly prickling in the heel and toe. I don’t imagine the stepsisters were particularly adept surgeons. They would almost assuredly leave some fragments of bone embedded within the slipper’s soft lining.
Which, even more horrifically, makes me realize that this did not take place in modern times and these women split open their feet to invite pathogens from literally hundreds, if not thousands of other women inside themselves. If I remember correctly, they were blinded, weren’t they? That feels almost merciful. They didn’t have to watch their legs percolate and putrefy in pre-antibiotic Europe.