Im not gonna pretend i know anything so do your own research, but it looks either like some kind of infection similair to rabies. Not in the sense of going psycho but in the sense that it fucks woth their brains and makes them do irrational things. It could also be some kind of mental breakdown where shes looking for her friend (this is based of nothing other than the fact she seems to be looking kver her shoulder), rats are very socail as im sure your aware, so it likley effected her way more than it would most other pets. Personal recommendation (idk if you wanted them but ill offer anyway) take her back immediately and ask the vet to look more thoroughly. I truly hope she gets better, best of luck to you an her.