Like April I'd suggest a live feeding if this snake is consistently refusing f/t and is getting skinny. A young adult mouse should do nicely (not a huge old exbreeder mouse....they can get really big). Please make sure to either ask questions or review threads here on safe live feeding procedures first though so that you are handling it well and watching Mouse for the proper reactions to live prey. I also feed in their home enclosure and believe, especially with live prey, a snake needs to feel safe and secure when hunting and that's best achieved in their own environment (just my opinion though folks).
As always, when it comes to feeding refusals...please double check your husbandry and consider getting a fecal done just to be safe.
~~Jo~~