Try smaller prey, it will be much easier for the snake to safely take down. 1-2 weaned rats is ALOT easier than a huge medium/large rat, and also not as fatty.
Just because she CAN take something that large, doesn't mean she needs it. She will gain weight and do just fine on 50-60g of prey a week.
One of my females laid 6 eggs in late May. She weighed around 1350-1400g afterwards. On only 3-4(about 20g mice) medium adult mice a week, she is up to almost 2200g, with barely any fat layer on her.
Smaller meals every 7 days will keep her feeding consistently.