Please get her on f/t (or freshly pre-killed) adult mice A.S.A.P- as bites from mice OR rats can maim or kill a snake when the inevitable slip-up occurs. The veterinary
care to patch her up from such a bite & fight the infection can get expensive, not to mention painful for the snake. There are techniques to transition a snake that is
only wanting live, but please do consider this.
F/T -either mice or rats- is the way to go. You must thaw correctly though & warm the prey up just before offering (use a blow-dryer), so the snake thinks it's alive.
Mice have as much nutrition as rats...it's just that an adult BP may need multiples to be fed adequately...it's only a convenience issue. And btw, I had pet rats long
before I ever got into snakes, so I get where you're coming from. Plus live rats are far more dangerous to your snake.
Depending on what she weighs- her current size- she doesn't sound all that under-fed to me if she's been consuming one adult mouse per week. It's often
healthier for a snake to grow slowly & it's preferable they do not pack on excessive fat...some owners over-feed their snakes & that's not good either. At
a year old, I doubt that what you've been feeding her has been harmful (as in far too little) & you're obviously a caring owner. I'm glad you came here to
help you sort this out.