Congrats on your new pal. I think it's great that you rescued a needy snake, so kudos to you on that. Now as for the new snake, so far she seems healthy. A three month fast seems like a long time but it's not life threatening. Snake metabolisms are so slow that they can afford not eating for a few months at a time and suffer no ill effects. Considering she's not dehydrated or thin as you said and has just eaten, it's reasonanle to assume she's on the mend. Just keep an eye on her to make sure she's not stressed or uncomfortable. If the person who had her before you kept her in poor conditions that may have been the reason for the long fast. Plus balls can be very picky eaters. Mine only eat when it's completely dark and no ones around. As for the growth issue she sounds to be of normal size for a yearling. It's been my experience that growth stunts or abnormalities are usually related to vitamin/mineral deficiencies. Since mice are a complete meal for a ball and no supplements are really required I wouldn't worry. It's good for young balls to eat every 7-10 days and then every two weeks when they become adults. It is possible to over feed so I wouldnt reccommend trying to compensate for the three months by feeding more frequently. Establich a schedule and stick to it. Finally it's always a good idea to get a stool sample and have it tested for parasites, escpecially if the animal was wild caught or in poor conditions. Find a good herp vet. Most run of the mill small animal vets don't have much any experience with herps so find a specialist. Good luck. Hope all this helped.