MC isn't officially archon. Their co-archon understanding is more of a personal thing between them. Sharon and Astrid were past lovers. She obviously still has a soft spot for her and doesn't want her to get mind fucked by Calisto. Sharon is prideful but also full of self doubt. She understands the real game already. She knows it didn't make sense for her to become archon at this stage based on just her influence and achievements. MC already confirmed it with her. She also has a needy side where she wants validation from MC and wants him to nurture her. She already understands that MC is on par or even above her at this time, but wouldn't outright admit it. She is a probably the character with the most depth in this story so far considering every other character (save for maybe Carmen) is one dimensional.
The dev is trying really hard to cut down on routes. It's unfortunate, but that's just how this game is designed. We don't see any persistent changes in Sharon's character or relationship with the MC. We just get a few alterations when the variable is called, but she goes back to the common script and follows the same progression, it seems. I remember reading someone's post a while back about the ramifications of the dev's coding and design choices. The game is essentially entirely "on the rails" and it will likely remain so until very far into the game. Major plot altering characters cannot be subjected to the players whims, as that will lead to branching. This is pretty much why Laurie is a nonfactor in the story since she is "marked for death" by that one variable. That's why Carmen doesn't really do anything since the player can romance her or not. If the Astrid choice doesn't merge back into a common plot thread, we can expect her character to be relegated to unimportant side stories that can safely be skipped. It looks like Sharon's reaction to that choice is already merged into the common route. That's not to say that the variable will be meaningless. It will most likely be called at certain points when the dev wants Sharon to react to it again, and it might even factor into a major branching down the line if the dev is ready to implment such a thing (For example, an extremely unlikely example of a huge branch might be Sharon betraying you vs staying by your side). The more likely scenario would be to just move on and let Sharon forget how mad she was about it for the majority of the script and maybe just call it for some flavor dialogues or minor alterations in events that merge back into common route again.
I started replying to your Sharon pride line of discussion, but it kinda went way off into a tangent. Sorry lol.
