I have the same issue. If you're going to give a treat, ONLY use carrots or something very very low calorie. Possibly a couple cheerios. Most of the packaged treats are pretty high in calories. Honestly i would just cut treats out all together.
Make sure your measuring how much food you food her. Losing weight is as simple as calories in versus calories out. If shes not losing weight after 3-4 weeks, and your not able to excercise her more, all you simply need to do is restrict for intake a little more. You have to measure and know exactly how much your feeding her though.
Also make sure she isn't diabetic or has thyroid issue. Ask your vet for help. You can sub out 1/3 - 1/2 of their food w/green beans, but that is not a long term solution. Let us know what you end up doing. How old?