first, if your not familiar with symptoms of MBD, then try and find some images of waterdragons that have it for comparison. I am not saying that you waterdragon has it, I just want you to be aware that there are other health relate issues that can make a waterdragon look obese. With MBD, an animal can look quite fat and even bloated, with a fat tail and thick limbs. A sure sign of MBD is thickened limbs that seem difficult to move accompanied by jerky movements. Anyway if you are sure that your waterdragon is healthy then weight loss is the same as for you and me, less calories, more exercise, with an emphasis on exercise. Waterdragons, like many lizards are really good at lowering their activity to match the amount of available food, so while you are feeding her less, she is moving around less to compansate. Try walking her around the house with leash, not out side unless you are confident that you can recover her if she gets loose. try feeding her insects that are harder to catch, like crickets or locust. For mine, I will find a big empty room and let a few crickets loose and watch them chase them down. Mine will work really hard for them and probably burn more calories then they get from eating them.