what size mouse is right?

[smrts1080]

I have a gopher snake she's about 2 and a half years old, 5 foot long and silver dollar size around at her thickest.
about 6 months ago I tried moving her to XL mice about 50-60g each as she was eating two large mice that are 25-30g each. she stopped eating them, I tried moving back to large mice she only took them intermitantly. I have now gone back all the way to feeding pinkies, she took them rapidly, moved up and up now back to small mice and she is eating 5-6 mice in a meal at 10g each. should I just try to move back to feeding two large mice or stick with feeding the small ones. is there a good way to make sure she will take larger mice?