Well first of all is she a she or a he? You have mentioned both. Females are generally bigger than males. I'm just gonna assume female.

I personally think you are not feeding enough. I would stop with the three really small mice and start going for adults. Right now my girl is around 275 grams and she is only four months old. But growth rates vary so I dont know how much you should compare. Try and get adult mice that are around 10-15 percent of her body weight. If you could get a good 25-26 gram mouse that would be great. If she thinks they are too big then 20 would work too. Also, how frequently are you feeding her? Right now you should be feeding around every 5-6 days.

p.s. dont worry if you feel like a dork bringing your scale in to get weights of mice. If the people at the pet store look at you weird thats their problem lol.