The problem with Serini

[KorvinStarmast]

I can't possibly see how that would make any sense at all.

That's at least two of us.

The two members of the OOTS least likely to be fooled by someone are Haley and Belkar. Considering both of them are with Serini, I see zero chance of her fooling both of them.

Concur.

If Serini decides to join the party, it's most likely it is because she decides all 9 of them together would stand a chance against Xykon.
If Serini were to betray the party after joining them, it would most likely be leaving the minute everything goes to hell instead of sticking around until the end.
It would not be any form of sabotage, as her endgoal is keeping the Gate, her body, Sunny, and the rest of the world safe in that order, followed by destroying Xykon. Betraying the order to Xykon would risk all of those, and if she decides the Order has to go away, she can do it herself, like she is now.
If it's the actual final showdown and things go south, I doubt she would try to flip sides or hinder the party in any way outside of getting out of dodge.

Serini gets nothing out of Xykon actually winning, and even less out of betraying the Order to Xykon. She doesn't work for him, and hates his guts. She's scared of him, but that doesn't mean she wants to throw bodies in his direction as a treat.

Said what I was thinking, thank you.

Is she going to make them blush?

Wait, is she a rogue or a rouge?