Going into the final battle with Namor, Shuri finds herself in the exact same position her brother was in nearly a decade earlier when he pursued T'Chaka's killer (both when he thought it was Bucky Barnes and after learning it was actually Helmut Zemo). Like T'Challa, Shuri too had become consumed with vengeance— and like her brother, she too recognizes the futility of the Cycle of Revenge and snaps out of it during the climax. Also, her mom showed up in a vision and told her to show Namor who she was.
Yeah, my issue is that
1) having Ramonda show up like that is not how the Ancestral Plane has worked before, so it felt like a cheap way to get Shuri to change her mind, and
2) aside from mom showing up, nothing else in the movie indicated that Shuri would stop right at that moment. Like, M'Baku even explicitly said that her mom wouldn't want her doing it, and Shuri rejected that.
Shuri being vengeful makes sense in the story, and I thought it was compelling. But if you want Shuri to change her mind
away from vengeance, I dunno, maybe she should have lost the fight. Maybe Namor should have yanked her off the spear and carried her to the Wakandan ship to show her, "You thought anger would be enough, but you lost the fight, and now your choice is to be our ally or be destroyed."
That would totally suck as a heroic debut for Shuri, and would be a naughty word way to pay tribute to Chadwick Boseman's T'Challa, and it would kinda feel like a retread of Killmonger's arc in BP1. Another option could have worked if they had set something up earlier in the film, but by that point in the story, I didn't see anything that really would change Shuri's path. Her turning away from vengeance at the last moment felt
entirely un-earned to me, and it kinda ruined the movie in my opinion.
(Plus the Ironheart and Midnight Angel suits looked like Power Ranger costumes.)