I couldn't immediately recall based on the angle in the screenshot, but from a frontal image and with the same type of clothing (i.e., bra and dress), it is definitely the reverend mother.....
I think it might be more or less the 'uniform' of the temple mothers.
I think ZetanDS is planning to add some paths in the game where you can "soft" the queen and convince her in a peaceful way,
If this game story is going anywhere (so far, sorry, but it isn't, where are more in the prologue than in the first act) i presume the whole optional alligiance with mutants and raiders is supposed to go toward a more multicultural zetan society in order to be better fit for survival. Inbreed and no technology are not much for the long game...
While rejecting alligiances probably implies a more despotic and purist society.
I mean Zaton will probably fuck her and even turn into her King consort in the future.
Could be, but loyality to Zarah is a big point of Zaton characterization. I think this might be a far shot or a plain evel route.
Also, there is a possibility another girl could become the new queen, like Shani, for example.
I don't see why, even assuming the zetan royality is not dinastic. I think the story is more about making the current queen a more self confident and just ruler (or eventually a puppet tyrant in a dark path). Having Shani crowned... i presume there are better claims to the throne in any case, even if, let's say, for some reason the queen dies or she is deemed unfit for the role. Shani is just a stalker.
The point is if the story want's to make actual sense or just be a payoff festival where the hero gets everything.
Kinda like the people who complained that at the end of Game of Thrones (i know, sad example) Jon Snow didn't become Kind of Westeros.
But if you want the story to make sense he is the very last person fit for the role. Not that he wouldn't be a great king but:
He betrayd the Nightwatch and his vows several time
He deserted (twice)
He crowned himself King in the North, betraing the Seven Kingdoms crown.
He bent the knee to Daenerys betraying his bannersmen who suppored his crowning
He marched south with a foreign invanding force
He supported a mad queen in slaughtering civil population
He betrayed his queen and commited regicide
And if that is not enough... He is a Targaryen, so he might well turn to be another mad king.
So, who in his sane mind in the Seven Kingdom would support the crowning of King Jon?