Red dwarf is one of the non-cold hardy bananas out there and in Southern California just until recently we've had temps still in the 40s which Red Dwarf's hate!
It's good it's inside. If you think it's been overwatered, it most likely has been. Now that it really has no leaves, it almost needs absolutely no water at all.
If it was only 4 in tall, it is possible it will not make it. The soil needs to dry out if it is to have a chance. Put the pot inside another pot that always dirt on the bottom and on the side to "wick" the moisture away from the pot that you're banana is in. Get it as dry as possible and wait for real growth before you even think about watering.
Z