Help! Major hermit crab after molting problem! Please help!?

i would not doubt it was the other hermit crab that dug up the molting one and mangled it ... they will cannibalize each other in the right instances ... that happened once in one of my tanks ... the substrate was not deep enough and one hermit crab i found had dug up a molter, already had a limb removed, and sadly that crab did not make it ... if this crab is 6 years old and has molted successfully for years, there is a chance she will live ... make sure the crab has everything needed especially a good calcium supplement, good fresh food including meat, veggies and fruit ... fresh and marine water ... try to watch to make sure the other crab does not go for the other one in her weakened state ... if you do see the other one picking on the mangled one, put in a tank divider to see how the injured one does ... good luck ...