She's feed rat pups not mice (rats pups however are about equivalent prey size to an average adult mouse). You could try giving her two rat pups per week and see if she likes that, she'll quickly let you know if she's not interested in the 2nd course or if she's still hungry enough to grab it up and snarf it down. Our male BP who is 10 months old went from 2 rat pups per week to one weanling just recently but he's a pretty big boy for his age lol. After awhile on 2 rat pups per week you could then move up to a small wean or whatever would be appropriate depending on your own particular snake's growth.

As far as judging the right size of prey you can even take a shoelace and lightly encircle your BP's widest girth then compare it to the widest part of your rat (which should be it's hips/butt end area). Aim for something that's about the same size or thereabouts. I like our snakes to look like they ate but not have a big engorged lump of prey in there.

One thing to watch is how old those rat pups are as a pup at 13 or 14 days old is a lot smaller then a pup of 20 or 23 days as it approaches the weanling stage.