Nothing of what she did couldn't have been replicated via other, better means, which makes her presence entirely superficial. If her role were likewise intended to be superficial, this would be fine, but given that this was supposed to be one of her grand schemes, it's entirely underwhelming. Given the lack of influence Graendal actually had on events, I am inclined to suspect that she was a late addition to the storyline, rather than a planned contribution.

I disagree that her survival was a deus ex machina, however. It was actually surprisingly credible, and this coming from someone who had strongly argued that she was dead.