I have had some trouble recently with 2 out of 50 ball pythons. One was a large female so I wasn't to worried about her. The other was a early 07 female who is about 254 grams. Which is tiny for her size! Shes had been on and off feed but on her last stretch went about three months off feed.
Needless to say I tried everything with her, before hand she was only eating rat pups but had stopped taking even those. The bigger female I was only offer pre killed rats. I offered her live and she took. The little fire girl I decided to assist feed.
The assist feed stressed me out the snake was flailing around and she was deathly thin and weak. I used a live rat pup that had just started to get hair. She ended up taking it. Three days later I tried a live small rat and she took it instantly! Now she is eating small rats regularly. I see allot of bigger guys on here saying don't assist and that it's not a good idea. But it may just turn your ball around and get them to feed I would recommend it to anyone as a last resort.