I said in here before....Mel, as the "holy crusader", could come back to her community to rid it of the bad elements, like some type of activist for the Lord. She still holds it against Frank for killing her dad. I can see her being like "SOMEONE has to take him down, and it's gotta be me."
I just don't see the point of bringing her back for basically TWO scenes the whole season if they're not gonna use her again. She has plenty of incentive to go after him, plus now she probably realizes that he's NOT gonna kill her OR tell on her, which may embolden her even more.
Also....I wonder what next season holds for characters like Dallas and Black Diamond....or even Peaches, where will his allegiances lie? Or the dudes in Leon's projects....
Story arc wise, they can go ALOT of different ways next season.