I have noticed a big difference in growth between feeding mice and rats, even when they are both fed the same weight (ie 75g of rats seem to have more nutrition than 75g of mice). This is my experience and I know others will disagree, but in my experience it makes a big difference. He also might have been feeding her smaller meals than you are used to feeding your balls. However, 308g isn't too bad and I wouldn't worry just yet. If she was only 125g when you got her back, then I would worry. Just keep feeding her those rats and she will catch up.