Underweight?

I just recently adopted a female bp from a family who couldn't take care of her anymore. She is 6 years old, but only about 300g. This seems really low compared to other weights of healthy ball pythons I've seen. She is overall pretty small (i.e. doesn't look emaciated, just a runt). I feel like she should have grown more by now.
Her old family was feeding her a large mouse every other week. I was planning to give her one every week, but since I'm new to ball pythons I thought I'd ask what more experienced keepers think is appropriate.

If her age and weight are correct, then she has been grossly underfed. Most BPs graduate beyond the size of a large mouse before their first year and that's eating weekly. I would start by trying to switch her to rats, which are easier to get in larger sizes (most adult BPs eat small or medium rats).

If you just got her, work on her husbandry first and let her settle for a few days or a week. Then feed her a large mouse which she has been having to make sure she will eat for you. Then the next week, go get a rat pup (about the size of a large mouse) and see if she will take it. Once she's on rats, just feed her whatever size rat is about the width of her widest part and hopefully she will start growing for you.

If she was taking frozen/thawed mice, you can try a F/T rat, though you may have to try live first to get her to switch.

Thanks! I felt like I needed to double check since I'm inexperienced, but I was like 99% sure that she's waaaaayyyyyy too small.

She's been on f/t so I don't think I'll have to go live. I have a couple large mice in the freezer for while she's adjusting, then I'll switch to rats. :) The mice seem just a tad too small too. :/