I'd take the shed as an oportunity to switch to f/t, typically they get VERY hungry after shed. Make sure to pre-scent the area and all that good stuff, and get the rat plenty hot, she should tag it. If not, you might need to do "the dead rat dance", basically hold it behind its fore limbs (with tongs of course) and make it look like its alive (wiggle it close to the floor of the cage.) She shouldn't even notice a difference
If that doesn't work, however, get her feeding regularly on the crawlers(say once a week for a month or 2) and after shes feeding well try maybe once every 4-6 weeks to get her on f/t. Keep her feeding durring that time, but if you get a wild hair, try a f/t. Normally, since she used to rats already, she should know the scent and recognize it as food and go for it.
The switch can involved starving, so its good to do it on older snakes, but with some persistance you should be able to get her over to f/t no problem. I say getting her to eat is better then what shes eatting, for the time being.