I've talked about this before, but it's basically a huge psychological payoff.
Many of you already know I was involved with extreme patriarchal christianity. For that set up to function, it's necessary for certain women to keep other women in line. Attwood used the idea in a fairly blunt way with her 'Aunt Lydia', but in my experience it's much less caricature, more subtle.
Obviously, in christian circles, there's the specific mechanisms of holy writ and an invisible, almighty god to keep adherents in line more generally, but in practical terms, every woman will at some point have doubts about her subjugation, at whatever level.
Enforcing women will be the ones who use socialization to keep those women from acting on those doubts, and even possibly punish those women who do act.
It's not consciously done, obviously, or it would be so much easier to break free from, and any woman can function in this capacity given the right balance of reward/fear.
The idea is simply that enforcing women are strongly motivated to keep other women compliant, due to being given high standing by approving males, possibly privileges and certainly open praise, and eventually due to fear of losing that standing and facing ostracism.
It has a vital function in cult settings because, like any oppressed class, the danger for the oppressors is if an oppressed class begins to see it's true position and organize. So enforcer women will serve to short circuit that.
Now, clearly, cultic patriarchal christianity is an extreme example itself, but you really can extrapolate the psychology to many other situations where women are liable to notice that they are being treated badly.