I'm sorry to hear that she passed away so recently. Sounds like she was a trooper and would try anything.
Most rides that involve dangling feet require the removal of a leg prosthetic, because of the possibility that it might fly off during the ride. Some of the more intense coasters require removal of *ANY* prosthetic and won't allow people with casts to ride at all, because of risk of injury to themselves or others. As long as there is most of the thigh bone remaining on one leg, and the full thigh bone on the other leg (the restraint actually touches something on both legs basically), the ride is perfectly safe to ride without part of one leg.
I can't find any ride specific info for Disney, but this is part of the info for Manta at Sea World, to show how prosthesis requirements are typically described:
And for comparison, this is for the Shamu Express, which is the equivalent of the Barnstormer at MK:
I'm sure Disney has something similar, but I'm either just not finding the right search keywords to locate it on the website or it is info that is only available from Guest Services.