Hou-Ting really doesn't strike me as the bloodline of Kuei. They are completely different; heck, they're the complete opposite in some aspects. Kuei was not assertive at all; that aspect is the reason why he was easily manipulated by Long Feng. Because he was completely unassertive, Kuei felt the need to redeem his mistakes which led to him making even further mistakes, as seen in The Promise. Hou-Ting, on the other hand, is defined by her assertive personality. She rules Ba Sing Se with an iron fist and controls every movement of her servants to the point that her closest advisor has come to the point of fearing for his life every time he's near her. And need I explain their different viewpoints of animals?
Okay, now that I got my opening statement out of the way, I wanted to share the theory I came up with. Like I said, I don't think that Hou-Ting really fits the profile of the daughter of Kuei. And I don't think that, as unassertive and easy-to-be-manipulated as Kuei is (and he sought to change those qualities about him in post-ATLA anyway), he would allow a tyrant like Hou-Ting to rule Ba Sing Se after him, even if she really was his one and only daughter. So here is my point: what if Hou-Ting wasn't really supposed to be next-in-line for the throne? What if Kuei had someone else in mind but Hou-Ting worked behind-the-scenes and somehow wrote a false will that led her to taking the throne? (So kind of like how Ozai took the throne, but we all know that there tends to be repeats in history in the Avatar universe.) And even worse, what if Hou-Ting isn't really Kuei's daughter? I mean, Kuei may have not presented his real daughter to the citizens of Ba Sing Se like in a Lion King fashion, just announced to the public that he had a daughter without showing her face so Hou-Ting could have easily kidnapped/murdered Kuei's real daughter and took the throne while getting away with it. So sometime in Book 3, it's Team Avatar's job to expose Hou-Ting for the fraud she may be and give the throne to the right person? (We all know that Hou-Ting will definitely come back in Book 3, as seen by the revealed episode titles and the trailer for The Stakeout.)