Can we all agree that Adrian is handily the best regular witness character in the trilogy? Most of the other witnesses are very one dimensional. They show up, show off some silly gimmick, commit a bunch of perjury, and then exit the story exactly the same as they came in. They feel like caricatures. Adrian has a depth that no one else outside of the main cast has. She feels she could be an actual person.
Seeing her genuinely smile for the first time at the end of 2-4 was the most cathartic thing in the game for me, which is saying a lot considering how much of a roller coaster the rest of the ending is. Seeing her doing better in the next game is really sweet as well. It lets you feel the difference Phoenix is making in the world.