What size tub is the snake in? I second adding another hide for added security. Is the prey an appropriate size? It should be no bigger than the girth of the snake, hopefully a bit smaller. One of my snakes is very particular about the prey size, she doesn't like them nearly as big as the other two (in relation to their size). On the other hand, I've had prey refused because it was too small before as well.
Other tricks might include heating up the f/t prey hotter than normal (did the trick before), pre-scenting the area (leave the rat by the cage for a bit), or leaving a f/t in the cage over night while having the tub covered for added security. This really helped me with my finicky eater.
I'm going to have to disagree about raising the temperature. Raising it a degree or two was suggested by my vet, and it worked wonders.
Also, your snake won't poop between every meal, so I don't think she not digesting fully is the problem.
I wish you the best of luck! Picky feeders can be a real pain, especially when you were hoping to have them up to weight for the breeding season
EDIT: Forgot to ask, do you feed in a separate enclosure? Keep us updated; if that doesn't work, there are other things. I've tried everything under the sun, haha.