GiftOfLove
From the Heart
It is sustainable, actually, if you're transfering that grief back into grief seeds, and then killing the newborn witches to reuse their seeds.4-5 marbles per hour, she needs to maintain her shades.
A typical cleanse from a grief seed is about 2-3 marbles. A grief seed has 1-5 cleanses.
A typical magical girl needs about one grief seed every week or two.
She needs 40 to 400 grief seeds per week.
That is NOT sustainable from "holding a city".
She's putting those grief controllers powers to the same use as their original owners.
Course, the witch probably becomes even stronger from all the build up of grief, but an army of magical girls probably don't give a care about that.