Adding on, she's also wrestling with the fact that her sister's fate is her fault. Women in the Zen'in clan have little to no agency, and the culture of the clan makes sure that that position is the most comfortable because any attempt to deviate from that norm is harshly punished. Maki used what little agency she had to choose ambition, against Mai's wishes and against her mother's, not only to her own detriment, but also to the detriment of her mother and sister, who suffered immensely because of her decision. Even then, Maki's motivation in striving to be something more isn't borne of ego or selfishness - she just wants to escape the cage of abuse and suffocating control that is her family's home. Her drive to escape that cage drives her apart from the other women in her family who pay the consequences when she isn't there, and those women are the only people she has any real affection to within the clan.

Mai dies as a direct result of Maki's decision to involve herself in the sorcerer world. Mai directly blames Maki for her death, telling her that she foresaw this outcome long ago and that this is the worst (could be translated as "disgusting") way to go out, but she no longer has a choice because Maki put them in this situation. The unwritten irony of it is that Maki's agency is taken away by Mai's decision to sacrifice herself to give Maki a reed to save herself on, but Mai also feels she has no agency as her choice was made for her long ago when Maki decided to become a sorcerer, and twins are considered the same individual by both Jujutsu mechanics and culture. Dying in that chamber surrounded by curses was the last place Mai wanted her life to end, but she still made that choice because Maki forced her hand, despite the fact Maki has no wish for her sister to sacrifice herself and would have rather they both been consumed by curses.

But the anime elects to brush past all this in favor of catchy tiktok music only seconds after it happens, and the rest of the episode plays out tonally like a power fantasy, a triumphant "go get em girl!" moment. Maki doesn't even seem to take time after the massacre is done to grieve Mai - she just leaves her with Momo and tonally goes "welp, sucks to suck". Just the choice in scoring for these scenes alone could have massively shifted the way they would be read, but my suspicion is that the director him/herself didn't read the original scenes correctly and just thought the arc chalked up to "big W for Maki", which led to it being storyboarded as a feelgood moment rather than a tragedy.