Like someone already said, some snakes will only eat when left alone with the prey overnight. Some respond better if you move the prey around to mimic a live rodent (I've noticed my colubrids are way more responsive to this than my BP, but it wouldn't hurt to try it). Also you can try blasting it with a hairdryer just before feeding.
I'd try live before going to the vet. If you've got other snakes, yes, offer it to her first. That way if she doesn't take it another will and you're not stuck with a pet rat.