[krackersmom2]

I am willing to bet she will change shells pretty quick without encouragement....especially if the shell is too small. My only paint that took forever to change shells was in the proper size, but in a chipped, super ugly shell. She has since changed shells.
In the even your crabby doesn't change shells, you can encourage her/him by putting the shells in a smaller plastic shoebox or some other escape proof container and put the crab in there with the shells for a couple of hours. If the crab doesn't change, then just have patience.