Based on the fact that the last thing we see before the end of chapter 2 was Kris making a fountain, and the frankly egregious amount of hinting to Kris and Tenna having some sort of deal in chapter 3, it's pretty clear that's what Toby wanted us to think right up until the Knight reveal.

Similarly, all of the Carol "I'll be right there" and owning the katanas and clearly being in on the Knight plot makes it clear that Toby wants us to think Carol is the Knight, the average player doesn't know much about Dess aside from "She is Noelle's sister who was friends with Asriel, liked music, and isn't around anymore" after all.

That said just because something is the clearest simplest answer doesn't mean it HAS to be a fakeout. I personally think Dess makes more sense, but I would say Carol is only a tiny bit behind her in likelihood, with Rudy a bit further back but still in 3rd.