Hmm, a few ideas. Sadistic heretek-priestess who just loves
to abuse fleshy meatbag bodies, Tzeentchian ratling who is all about making deals and coming off better so that she can pursue her true secret goal of
, and, depending on how icky and sexual we want to get, Nurglite woman, maybe a former SOB who carries (and spreads) a new variant of the zombie plague through a certain swollen and tainted part of her body that happens to be between her legs, or through fresh, tainted milk.
I'm leaning a little Nurgle, although that'll be best if everyone's cool with it because, well ... Nurgle.
Edit: Leaning a lot Nurgle, since ideas for the Plaguemother keep
turning up in my head, like her sincere, honest belief that guiding worlds to her plague-filled tea is the kindest thing she can do for those benighted children who languish without the love and blessings of Grandfather Nurgle. Of course, still Nurgle, so ick-factor is there.