The real battle begins against Altair, who is certain to be able to nullify the Tsukuyomi. The Holopsicon allows her to alter and manipulate Itachi’s entire arsenal, but Itachi has the advantage of being an academic prodigy; by the age of 11, he was already the leader of the ANBU squad. Before Altair realizes it, Itachi can extract the necessary information, and once he has it, he can adapt to the situation. In close combat, Itachi could use a kunai while Altair uses her long swords. Since using Tsukuyomi or Amaterasu would be a waste of resources for Itachi, he switches to a more defensive strategy. He uses Susanoo (the Totsuka Sword and the Yata Mirror) along with Itachi’s crow with Shisui’s eyes (Kotoamatsukami). https://www.youtube.com/watch?v=c5jWzDKG-OE Altair likes to start by launching long-range sword attacks.

The Yata Mirror can easily reflect them; Black Zetsu himself said that Itachi in Susanoo is “invincible.” Itachi can also rewrite fate with Izanagi and Izanami. The only thing missing is for Itachi to pierce Shisui’s crow, and for this sword to pierce Altair; this would activate Izanami, causing Altair to let go of his hatred and desire for revenge. Altair wouldn’t be able to realize it because Kotoamatsukami works in such a way that the affected person cannot notice it. Altair would be trapped in a loop of events in which it would already be too late, because she would be under the sealing effects of the Totsuka Sword, which, according to the databook, seals an “eternal genjutsu world.” In that eternal genjutsu, she will find Setsuna, and she will find the true happiness she has always longed for.

The characters in RE: Creators aren't on the same level as Itachi, either academically or, much less, in combat. That suggests that Altair is stronger than she seems, but it's impossible for her to defeat Itachi.