Wow thats a tough question! So many different things can account for the girth, sex, YES PLEASE!, age, diet, prey size, length.... Balls will become over wieght if fed to much but sounds to me that yours is doing just fine!! Once a week feedings are a good way to go and if your feeding mice i dont see how she could be getting to much unless you are feeding multiple mice a feeding. Davu is 30 inches and i havent thought to measure his girth but I will do that when i get to the house tonight and post his measurements!
Sounds to me like your good man, just tell him to cut back on the french fries and milkshakes and you should have no worries!! lol