Why would you be switching to Mice? If she's eating rats now... its just easier (IMO) to continue feeding her Rats. It would take quite a few Mice to replace what she's getting with two rats.... and if you ever wanted to turn back to rats in the future... she may get "addicted" to the mice... They're imprint feeders, and mouse feeders just seem to want mice... and only mice.

Just my eight cents..