First, welcome to Fish Lore Krista
If your fish is cared for properly and not bullied by other fish, it should grow its fins back. Can you tell us more about the fish? Do the fins look as if they were torn away from its body, or do they look "withered" as a result of some disease? It would be either that other fish did that to the shark, or that it has a fin rot. You need to know which one of the two scenarios it is.
Besides, how large is your tank? What other fish (and how many) do you have in there?