Nebula got to have this cathartic experience, which could be seen as the end of her story, by helping the Avengers to defeat Thanos. So now the source of her abuse and pain is finally gone for good. Nebula also took a page out of Kylo Ren’s book. Adam Driver’s Star Wars character said to let the past die and kill it if you have to. Well, Nebula had to and did just that, literally killing her past self, the self that was broken and manipulated. Now she can become who she was meant to be.