Help! Is my ball python overweight or underweight?!

[Bogertophis]

...If I go to medium should I continue to do it once every 2 weeks or more often to once a week?

First off, there's no point changing to mediums if you feed more of them, is there? I agree with GoingPostal & bcr229's posts above. Her refused meals are telling you something- it's up to you to listen.

"Scheduled feedings" are only a reference point for snake owners- it's not how snakes eat in the wild, & remember that in captivity, your snake is far less active than they'd be in their natural world.

If your pet refuses a meal, go longer between meals. It's no problem for yours to eat once every 2 or 3 or 4 weeks apart- ie. when they need & want to. Pushing larger rodents on your pet than they should be eating often results in them fasting, which is frustrating for the one feeding them- especially since you'll be buying & wasting a lot of food- not to mention, worrying. Feeding small or at most, medium rats for adult BPS seems to work well for most keepers.