She isn't. The thing that makes Lapis especially awful from every single other gem is that she never gets any consequences for her actions. Every time any other gem does something wrong, even if they arent properly punished for it, there is some consequence for it or at least an acknowledgment of how fucked that character's action is. When Pearl fused with Garnet out of trickery, there was a whole arc where she suffered for it. When Amethyst shapeshifted into Rose, she ordered Greg's stuff to apologize for it. Anytime Peridot says something offensive or stupid, she is criticized for it and has to apologize. When Garnet's future vision puts Steven in trouble, she apologizes. The Diamonds had to restructure their whole empire in a way that has not satisfied them. And I don't need to tell you how much Jasper has suffered for her crimes. There is repercussions for everyone's actions, except Lapis.
Lapis hasn't gotten better because she went through proper development, she just got better off-screen and because the writers wanted her to be with the good guys quickly. Her friendship with Peridot, learning to love Earth for its nature, the resolve to fight for her friends on Earth, apologizing to Peridot for leaving her (if she even did that) all of that was off-screen. There have never been any meaningful moments that showcased Lapis growing as a person because every time she does something wrong, Steven forgives her. She barely has any relationship with any crystal gem (Bluebird has had more interactions with them).
This episode is a testament to how awful of a character she is, and cements the fact that there is no hope for this character. She will always be a mess.