Reading over this highly interesting thread gives me a wicked idea that is tantalising to entertain.
Why were the istari limited to old men? After all, the species Men includes women. I think
Esty's REB III deserves to have an old female emissary. Maybe she even suffers from the wretched injunction not to use her full powers but always to defer to male authority. Yes, yes, fifty ways to keep a good woman down.
Now that's a possibility to ponder . . .