I Remember When Whining About Her Age Was One Of Sam's Primary Bits.

 It's the Day's Day of Days! Because youngblood.

There are two interesting aspects to Xir coming back like the jobber heel in a wrestling match to get stomped again. One of course is that Muir is clearly trying to replay the "high" of Sam's victorious campaign for council. The campaign after all required effort from Sam, and let Xir be an actual opponent. Not much effort on Sam's part--indeed, a parody of effort--and Xir's efforts to win were laughably incompetent, and served as nothing but a demonstration of their inferiority. But once Sam was on the council she was the de facto dictator of Gunpowder, able to make nonsense happen on a whim, and Xir was even more of a punching bag, now utterly powerless against any shit Sam did to make their life miserable. This is clearly an effort to go back to that dynamic, all while ignoring the essential problem--victory comes to the cast unearned, against laughably incompetent foes and merely grants them more victory.

The other is that now, Xir is apparently a wealthy member of the elite, something that was nowhere previously indicated. It fits with their protean nature--about the only clear thing about Xir's gender and orientation is they're not straight, and they at least somewhat identify as a woman. Now, to better be the insidious and decadent elite, Xir is rich. But the bad kind of rich, because they don't support fascist values.