I am not willing to sacrifice any of my waifus (as each lair requires a different waifu to be sacrificed)
You are not at all required to sacrifice a waifu to proceed with the game. Indeed, I have tested and it is possible to conquer the lands without having them pillaged and still collect every girl, all while disregarding your lair's faction. Though you likely will have to settle for mina being unhappy.
On the subject of Valzira - here is what may likely be an unpopular opinion: I really like her.
Her character has much in common with Naho who has plenty of fans so that makes her lack of more public appeal doubly puzzling for me. She's working the defiant
"sound and fury" shtick marvelously, her speech is one of dignified contempt and those characters go a long way with me. Particularly the scene where she demonstrates willingness to suffer what is apparently unspeakable pain just to spite you. First time reading it, i was genuinely awed with the gutsy gamble with her own life in order to deny you, never relenting on the insults even in the throes of agony.
Love the "bound, but not broken" bit; attempts at appeasement, or threats are met with defiance, bile and disdain. Which brings to mind a very fitting quote:
"Hatred is as good a thing as any to keep one going. Better than most"
That is not to say I advocate for her to become a consort option, though. Doing so would be breaking character. Valzira's appeal - sadly - also means that she cant fundamentally be cowed or reconciled with, and thats how it has to stay.
And thats alright - there are already plenty of characters who can be brought to MC's way of thinking, one way or another, and it's good to have one that wont compromise.