Does she eat every week, or does she refuse a lot?

If she's truly eating 4 adult mice a week, then I'd be concerned about internal parasites at that weight. I easily raised most of my females to 1200 grams and higher on just 2 mice a week.

I'd recommend taking a fecal sample into your vet to rule out internal parasites as a cause for her not to grow on 4 mice a week.