I think Sofia understood that even though Oz ratted her out to her father, there is no way he knew or intended that she'd end up in Arkham. But as soon as he admitted to killing Alberto, that was it for her.
Now, I will definitely agree that her believing he wasn't involved even after the kid said he saw his car there that night, that part is a bit of a stretch.
Now, I will definitely agree that her believing he wasn't involved even after the kid said he saw his car there that night, that part is a bit of a stretch.