Funny how people call her "bitch queen" and so on.
She just does what's most sensible to weaken and keep in control someone that's stronger than her. She has no indication of what he wants to do, and he's frighteningly powerful and intelligent. He could assassinate her tomorrow if he decided to, or dethrone her, and she's well aware of this.
She's made into the villain, but there's not much else she can do to try and keep the throne.