I would bet she is an older(2 plus year old) animal that hasn't been feeding very well and thus hasn't put on size. Snakes with scars that have been attacked by thier intended food often become sporadic/nervous eaters(for good reason). Sharing an enclosure with another snake didn't help either. Give her a hide so she can ambush her prey from a secure location. Usually once a rat/mouse starts walking all over a nervous eater they won't feed. I adopted a similar animal over a year ago, she eats enough to maintain her weight, but doesn't grow much at all.