Is there any reasoning for everyone being so cautious...? Id be offering small rats every 5 days starting with today. The whole "you have to wait a week after bringing them home before you offer food" is a myth imo. As long as shes in a proper setup she'll feel secure and be fine. Sure, some still do refuse on the first day, none of mine ever have though. Maybe im just lucky, i doubt it.
EDIT: By small i mean id offer something the same thickness that she is in her fattest part.