I'd say if shes just started eating again, keep with it for awhile. Then you can try pre-killed then over to f/t. Are there any other petstores around, if you have to drive 10 more minutes to get appropriatly sized rats, then maybe that is something you need to do.

Also about the soaking of the tank, you can always try to feed outside of the tank. My BP does it, and generally he ends up putting a hole in the side of the mouse, and during constricting blood/guts gets everywhere, which would be horrible to clean out his tank (I also take the time that he is in the feeding tub to clean out his regular enclosure).