I feed small rats to my mid sized snakes, even though many of them can eat larger sized prey items. It maintains them at a nice weight just fine. Consider how much they are eating and how regularly compared to the wild - even feeding a relatively small prey item every week is still better eating than what they'd get in their natural habitat!

If you're worried about her weight, feed her two in one sitting, rather than every 5 days.

During the summer, when my snakes are eating like crazy, I'll sometimes feed every 3 to 4 days for the big girls, especially if I'm just feeding them excess small or medium rats instead of a good sized large. That only lasts for a month or two at most (right after egg laying, actually) before things slow back down to a more normal 7 to 10 days.

-Jen