Could it be the core temp of the rodent?

Movement, heat and scent are the 3 things they need.

If she hits from the movement, is excited by the scent, but perhaps does not recognize the rodent as food from the temp drop following?

How are you heating the rats? I have a few of those girls, and they are the ones that tend to prefer live (and I know you do not feed live). Any live feeder that is converting, or any FT feeder that is giving me grief, I pay extra attention to that.

If you are not already I would suggest a good water proof bag to float her rodent in hot water, get the core temps up, and then hit the head and tail with a blowdryer (or heat gun) to mark those areas...

Bruce