i personally would start with rat pups every week and work your way up from there. new borns are fed rat pups and do just fine, it shouldnt take long till she sheds. after first shed you are going to notice a pretty decent change in the size of the snake, it may have a little bit of loose skin after that but it will fill in. my first snake was only fed 2 mouse pinkies a week for the first 5 years of its life and now that i have her, shes quite the sexy fatty lol.
good luck with the rescue