Advice needed

I have a 400 gram ball python that eats frozen thawed mice once a week. I have tried offering small frozen rats but she will not take them. Any suggestions on how to get her switched over?

Once they've been on mice for a long time, it can be tough to switch.

Here are some tips. Skip one feeding. You want the snake to be hungry and at 400 gr. it won't hurt to skip a feeding.

Thaw the rat as well as the mouse. Before presenting the rat, rub it all over the mouse one more time (I know how that sounds, LOL)
You want to get just enough "mouse scent" on the rat to make it appealing. Normally you only have to do this a couple of times. Before finally switching to a unscented rat (meaning no mouse scent on it) skip another feeding to make the snake hungry.

:)

Another thing you might try is offer a smaller than normal frozen mouse first and just as she is finishing the end of it, put a very small frozen rat item in its mouth and see if it keeps going. You need to make certain the size of both is not much more in total weight than 15% of your snakes current body weight. A couple times of doing that and it should get acclimated to the scent/taste of the rat.

At 400g they should be on weaned rats not small. It might just be too big? She won't be on weaned very long lol