The Real Villian

Although blackmail and cruelty exist, why would one not go for an easier option?

Deception. Kara's plan is simple and effective; she'll find an Authority-- a weak and young one, obviously-- and use them. Deceive them. She'll build their trust, their bonding, and then snip them off like excess string on cheap leggings the moment they become unnecessary.

It's a clear-cut agenda, there's no possible chance for her to go wrong. Unless, of course, the impossible occurs-- unless she actually becomes attached.

But surely that's impossible. No?