Two adult mice isn't enough. My guess is that she's probably long but skinny. I have a 6 year old normal female and she's 2500 grams. I wouldn't OVER feed her. Maybe start out with a medium size rat and build from there. I would image that her stomach isn't used to digesting a 140g rat so go smaller and work your way up. Give her 2 hides if possible (one on each end).