I would guess your snake is hungry from all that I have read and the little I have seen. If that is the case then you should be very concerned with the size of the food. Also they bite with their mouth and constrict with there body. If the prey is too small it would have to constrict with its neck. Ball Pythons will eat dead prey in the wild so maybe she thought it was dead already.
I find that the "thickest part of the body" and "10%-15%" rule are not mutually exclusive. My Ball Python is a little over 20 inches long. She weighed 101 grams before her last feeding and I fed her a medium mouse that weight 14 grams. The mouse was 13.8% of her body weight and about the same circumference as her. My snake usually explores her tank after being held and has fallen more than a few times. I recently went into my back yard cut down a maple branch, trimmed it to fit her tank then baked it for an hour at 300 degrees. Then I put it in my freezer over night, let it warm back up and then introduced it to her cage. With more stuff in her tank she hasn't fallen yet.
As for keeping mice in the freezer. I have a live in girlfriend that was very very against having a dead mouse in the freezer. I picked up my mice from Petco, they come in individual sealed zip lock baggies and those baggies are in a Tupperware like container. Try buying a pint of ice cream and labeling it PANDORA's. Throw the ice cream away and wrap the mice container in paper towels and then put that in the ice cream container. Put Pandora's "Ice cream" in the back of the freezer. Now if anyone tries to eat her ice cream they are in for a surprise.
People should no better than to open Pandora's box...I mean ice cream tub filled with paper towels wrapped around a container filled with individually packaged dead mice.