I don't really see any member of Kaidou's crew showing up yet. They would be there as backup to protect the factory not to get Ace's fruit. Considering the SHs are there to destroy the factory and Kaidou sorta needs it for a big shipment his has coming up. Especially since the underground most likely knows what happened at Punk Hazard with the SAD factory and Caesar losing. The last factory would take priority over Ace's fruit.
As for anyone arguing it can't be Rebecca since she attacked people and that doesn't fit her style since she only dodges. She is totally against phsyically hitting someone. You forgot something really huge that destroys that arguement. She's in this tournament to get a "fire" DF power so she can personally use it to defeat Doflamingo. A fire power is not really a non-physical type of ability. You can't really use it without phsyically harming the person you are using it on. So typically she is against it but when the times come she will use force. The flashback even alluded to this since LS was actually hitting her so she can get a real sense of danger and that's when growth actually happens. So if it was Rebecca, she was getting beaten bad and then unleashed a speedy final desperation move on everyone. Which would account for why she fell down after she did it and why she has bruises.
In that case, it's sloppy writing. Why not show Rebecca getting those bruises then? She looked fine a few pages before the "accident" (like everybody else).
But in case it was her, remember that it's not guaranteed that she's the one standing up at the end. Elizabello also unleashed an ultimate move that knocked down a bunch of fighters, but he wasn't the winner.