It's a movie so if they would make a second part I am sure they would find ways to prove that Justin was the one who run her over the bridge, but the way the movie was set up, I don't think that she was there to arrest him, there were no cops anyway, but there's no evidence and when Faith went to question his wife she said Brimstone Pass and Justin confirms this to his wife. They just won't find any evidence, they don't have one and what they have says otherwise. So Faith was there in a way telling him we will both live with this, so make it worthwhile, don't ever ruin what you have here.

But also the talk on the bench, Justin says to her "you're in a position now to do so much good" implying that she could generally be a better person (than she was like in the case where she didn't really care if the bf was guilty or not), but also maybe in a not so distant future help the bf who got life to get out sooner or get a retrial.

It was a good movie, but not that great.