With her hormones and everything being correct, the problem is simple. She is taking in too many calories and not burning enough. The solution is pretty simple as well, either increase her calorie burn(exercise) or reduce her calorie intake.
If you don't want to increase exercise or decrease her intake of food, then change foods from a carbohydrate based diet(chow) to a more protein based diet(meat).
Many people, including myself, will get in the habit of rewarding our dogs for everything with treats. When you, the kids, and the wife are all doing this, it adds up to a lot of treats. Minimize this habit or remove it all together.
Best of luck to you.
Gangly, you got it.....definitely the treats and human food. I have a puppy coming in a couple weeks and am afraid of this too. I eat like a fat azz, and it wont be fair to her for me to woof down food in front of her. Hopefully I can keep her ONLY on her recommended food amount, exercise her and let her swim.
I'm hoeing this will get me off my azz and walk , train, her everyday...