Weigh her food every time you feed her. Give a little less each day than what you normally serve. If, after a few weeks, she’s not starting to lose weight, reduce her daily rations a little further. The key is, you want her activity level to remain normal, but that she would lose weight slowly. I did this with our dog. She returned home alarmingly overweight after being boarded. I got her back to her normal weight within a few months.