Depends on how you play it. If you play sharing women and fucked Shani too, I can't see how sharing her would be out of character. The game gives us the choice to turn her into another one of our pets or to leave her alone. We can already start a potential sharing route with her and the Queen.
Sharing is not the same as "selling her ass" (as you put it).
I do expect Shani to be involved with others, outside the harem. I am fine with Shani being with the Queen, I'm not sure how I feel about other males, but I guess that if they are worthy it should be ok.
Shani is Zaton's heir, and therefore not a pet, not even Zaton's pet.
Shani's function and character is fundamentally different from Ain's. And with Ain, Zaton needs to force her to do stuff with Igor. This means that Zaton honours Igor by offering his daughter to him, clearly without Ain's consent. What Ain wants is more or less inconsequential to Zaton.
With Shani, that is different. Shani, even while sexually not very experienced, wanted the scene in the Baths.
