>She absolutely will not do any personal business in front of any human
 
Charlene,
    Perhaps you have already done this to augment your covert ferret
monitoring efforts :-) but since you didn't specifically mention this in you
post I'll -- for what it's worth -- share my two-cents.  You might consider
stratigically placing a mirror in the litterbox area so her behavior may be
observed.  Such a mirror would need to be placed at a height where she could
not in turn monitor you :-)
 
   This method has worked for me during the "post-introduction phase" of
ferrets we have added to the household.  Since they do not perceive their
two-footer around, they interact as if I'm not there -- meaning they have
no need to "show-off!"
    Irene & Koto, Etsu, Yuki, Moxie, and Mikey
[Posted in FML issue 1324]