Stop feeding her 3 rodents at once. Try a small meal next time after at least 10 days waiting, maybe only 1 rodent and maybe a little smaller too, for right now. Let her digestive system recouperate. Did you see any signs of her being gravid? Did you see ovulation? If you can determine that she is gravid, just stop feeding her.
How old is she? How long? Is she thin or fat? Have you been feeding her this much for a long time? How many times has this happened? What does the stuff look like, is it diarhea? Is it solid and brown?
I agree the feces was still from the previous rodents not the same ones you just fed. This means you are feeding her too frequently. Yes, wait until she has defacated and then even a few days before feeding her again, always.