Are you absolutely sure it was warm enough? Its sounds to me as if she got the scent, but maybe when she got her mouth on it, it was still cold inside?
You need to feel them or check w/ temp gun, & most here seem to have the best luck by warming w/ a quick shot from blow-dryer right before offering.
The larger the rat, the longer they take to thaw inside...and it's also possible she decided this was too big, though most snakes that are truly hungry don't
refuse on that basis.