Yeah you can definitely bump up the size so that you can decrease number of feedings per week.
Can you get rats? That will open up a whole new world of sizes for you.
Though if you can't you can also feed multiple items per feeding so that you are still only feeding once a week but she is still eating twice as much.
im sure my local pet store carrys them i will check the next time im there i still have a few mice left before i need to make a trip. ive heard that some people have a problem switching to rats is this true?