The breeder is saying that she has eaten live rat pups who are 14-18 days old.
http://www.rodentpro.com/images/size_r_pups.jpg

Is that the same size the f/t rat is? If not it may to big for her.
Also I take it you have only had her for a week? You may want to give her another week with no handling or anything and just let her completly settle in to her in home.

Also check your temps and humidity. 90-94 on hot side and 80-85 on cool side with 50-60% humidity. You can easily measure the temps by dropping by Walmart, Target, Lowe's and picking up a thermometer .

Another thing, did you just plop that f/t rat in there? You will probably have to make it do some kind of "dance". Get a pair of tongs and wiggle it in front of the snake. It may take a few minutes. Also remember snakes are nocturnal, so they do hunt at night. Some of my snakes will only eat at night while others have no problems eating while it's day light out.

Last but not least there is nothing wrong with feeding live as long as it is done responsibly.