For the first time, I'd try the rat just as-is, without any tricks or shenanigans. With the exception of one very, very stubborn pastel (who still only eats mice and he's 5 years old), the rest of mine all switched without any fuss or tricks.
If she doesn't eat it the first time, give it a week, and then try again. Sometimes getting a little hungry makes it easier, too.
-Jen