I have a feeling or maybe I'm just hoping that perhaps Rebecca will end up eating it and joining the crew. First off it would be nice to have a third hottie around (as long as they save the last spot for a fishman damnit! or an inanimate object LOL). Also I've always felt the SH crew needed a logia user around. She's already sort of set herself up to become Luffy's friend. Obviously she doesn't like Doflamingo and her and Luffy seem to be getting along well. I'm betting Rebecca is quite strong and has a mean fighting spirit which impresses Luffy. However I really doubt she'd be able to win the tournament even if it went into the final rounds, there is Luffy, Burgess, and the Doflamingos a very powerful group.
So here's the scenario I see happening in my head -
The tournament will be crashed by CP-0 and marines. A bunch of One Piece chaos ensues, and eventually the SH crew ends up in a big showdown with Doflamingos. Rebecca helps Luffy fight however is of course too weak to fight the big man himself. Luffy helps her get revenge, they recover the fruit, and Luffy offers it to Rebecca in return for joining his crew.
I mean lets face it, as focused as Law is on his little plan as soon as Luffy stepped foot on that island we all knew there would be a bunch of chaos and a big showdown. That's just the way it goes. Though Frank the Tank is like a fucking soldier when given a mission, he'll surely seek and destroy that factory if it is indeed on Dressrosa.
Of course things could go completely different at every turn. One Piece has felt especially unpredictable ever since they got into the New World. This is sort of what I'm hoping for but then again we haven't actually seen Rebecca's face or most of her personality yet, what if she's boring? Hahaha. I guess what I really want is a third hottie, but she has to be interesting and fit in with the crew.