Well, I don't think the Administrator is such a useless character, considering that she is, in fact, the main antagonist of this story (not the plot of Asuna and Inoda, but the global plot). To this can be added her words and actions - she considers Kirito the Chosen One, wants to meet with him, erases his memory of things that he does not need to remember, gives gifts (of course, it is not yet clear what kind of gifts), gives advice. Kirito doesn't understand these tips, but maybe that's the Administrator's goal - to keep Kirito in the dark for now, but to show more "anxiety."
Brainwashing is too rude, I'd say she's guiding Kirito in the right direction. Considering that the theories that Quinella is in Kirito's head and that she wants to be reborn in one of the bodies of girls who are familiar with Kirito may turn out to be true, I don't think the Administrator is just falling apart.
Brother, of course I can't know exactly the role of Quinella in all this, but a character who just trolls Kirito (the player) after every game day is kind of shallow, flat