There are many methods that work. Persistance is the key!

I have several methods but the one I always try first is below:
1 - don't feed her for at least 2 weeks (unless she is of course underweight)
this will make her hungry. She should be responsive to movement (ready to strike) this will be a sign she is hungry. Don't confuse this with a defensive hissing posture
2 - put some soiled mouse bedding in her tub to excite her about 30 minutes before the placement of the rat.
3 - put a small or weaned rat in mouse bedding, if you have to bury them in it, let them sit in it for a bit, at least 10 minutes. The longer the better.
4 - get a mouse and quickly wave it in front of the snake fast enough for her no to be able to catch it. Maybe just to solicit a strike.
5 - Imediately put the mouse scented rat in the cage.
6 - Cross your fingers.