While there is a nutritional difference the nutritional requirements are not known so gram per gram of prey it's all the same, the advantage with rats is that you do not have to feed multiples when feeding rats.
Given she has been eating 2 mice every 5 to 7 days I would likely do more of a 7 days schedule at that point.
Try getting an idea on the weight, make sure she is well hydrated, make sure your husbandry is on spot and most importantly be patient.
You can also try to downsize her to the smallest enclosure possible sometimes it does the trick.