Regina:
If there is a degree of separation, the author has a lot more to work with.
Well, of course ideally there should be no difference in "separation" between parents and an adopted daughter as opposed to a biological one, however it might depend on what age the girl was when the adoption occurred.
However, I do see your point, I often have my male characters spanked by stepmothers and stepsisters to provide a somewhat greater "degree of separation."
In the policewoman-catching-her-parents scenario, would the young lady believe that they had been too strict in subjecting her to spanking punishment during her girlhood, so she has an opportunity for some serious 'payback' on those parental posteriors?
Or would she feel that she didn't get the needed corporal correction which would have helped her develop a sense of responsibility and self-discipline earlier than she actually did, so she has an opportunity to demonstrate how they should have disciplined her?
This could be a compelling narrative if written by the right author...

--C.K.