I have to wonder who was hotter... Niao Sun or Li Feng?
Well I mean Niao Sun
did burn the castle down, I guess you could say that was pretty... HOT.
I'll let myself out.
Her appearance inspired more trust. Shenhua at one point tells ryo she was asking all sorts of questions about them. So not random at all unless you ignore the above.
The reason this twist doesn't work is that we have no reason to suspect anything is going on and we have no context as to who she is. If you want to see a twist like this done well, you should watch The Usual Suspects. In that movie we understand who both characters are (one is a cowardly narc, the other is a ruthless drug lord) and why it's so unlikely that they're the same person. The mystery of "who is Keyser Soze" is also central to the plot as opposed to Shenmue 3 where you have no idea who Niao Sun is or why she's important even after the reveal.
For it to work in S3 before the reveal we'd need to know, at a minimum:
1. Who Niao Sun is at least by reputation (say she "runs" Niaowu the same way Dou Niu ran Kowloon and she's known for being a seductress)
2. Who Li Feng is (she's a kind-hearted mother figure who helps Ryo)
3. Niao Sun needs to be central to the plot (she works for the Chi You Men, knows where Lan Di is, and wants the Phoenix Mirror)
4. Li Feng needs to not be central to the plot (she hangs around the background and helps Ryo after fights or something so Ryo actually befriends her/ lets his guard down)
That way when the reveal happens we have enough information to connect the dots and be surprised. As it stands, when Niao Sun is revealed, there's no sense of betrayal because Ryo never trusted her and there's no sense of surprise because we have no idea who Niao Sun is (she's not even named ffs).
TL;DR it's fine if you liked it, people liked Daenerys' turn to the dark side in Game of Thrones, but that does not mean that it was properly set up from a storytelling perspective.