How much does she weigh? How big is the enclosure? How many times have you been handling her? The majority of feeding issue with new owners how 98% Husbandry related.
The best way to offer frozen to a snake is to thaw at room temp, warm up with a hair dryer and grab it from behind the neck and move it around as if it was alive.
Putting a f/t rat with a snake for 36 hours only contribute to more stress if the animal does not want to eat, overnight is more than necessary already.
Now the issue is that if the animal was not eating F/T in the past you may try to convert an animal when you should really have the animal to eat for you successfully first and for at least 3 to 5 times.