My first thought is airway obstruction? Has she eaten something and it got stuck in her esophagus impeding her breathing, perhaps? I don't know how to help, I"m sorry
I'd call up emergency vets and see what they'd say. Other than that, I know rats are prone to lung infection or even permanently have some lung illness that flares up periodically, so perhaps she has one and is in a bad state now because of it.
P.S.: try rat forums!!!