Can you weigh her? If she does go on a fast, that's good to know so that if she does start losing weight, you can at least tell. A postage scale or kitchen scale isn't expensive and will tell you.

Are you sure about her size? 1-2 feet is a pretty big range, and also pretty small for a 2-3 year old ball python; 12" is like hatchling size. Length isn't necessarily that useful of a number, but if you want to find out you can try www.serpwidgets.com to measure. You take a photo of the snake next to a ruler and then follow the instructions.