It can be difficult to know when enoughs enough , from experience i know some ferrets dont do well when there being got at .
I use a few simple pointers , if the ferret on the receiving end of the punnishment starts to drop weight , loose condition i remove it , constant attacks from other ferrets can & does depress there cage mates if its allowed to contine unchecked
All you can do is observe there squables & if you feel the jill isnt fairing well then remove her