^^^What Zincubus said!^^^ Zincubus suggested this to me as well when I was having problems. I started using a heat gun to heat up thawed rats and a couple of my snakes that were driving me crazy refusing f/t immediately started eating and have been eating like champs ever since. Not only that, but the smell of rat, which fills the room from blow drying each rat at feeding time seems to send every snake in the room into a ravenous feeding frenzy! If she shows interest, but doesn't take it right away, just keep heating it back up and offering again. Don't give in and give her live...
PS Don't thaw your rats directly in water. Either just let them sit out for a few hours or make sure they are sealed in air-tight zip lock bags, if you're thawing in hot water...