Sakura has enough physical power to break through Susanoo so we can forget about Kakuzu tanking repeated hits or her strongest hit. Katsuyu alleviates the pressure that's put on Sakura by having to fight 2 shinobi at once since they don't have the means to kill it, making it a good shield and can spray Acid at them. It won't hit them if they are paying attention, but they still need to dodge which makes it easier for Sakura to land a follow up blow. The majority of Kakuzu's jutsu can be straight up tanked, what can't be tanked can be evaded or overpowered, and if he tries to bind her she overpowers him, reels him in and clobbers him.
Once Kakuzu falls, the match might as well be over as Hidan is a fodder in comparison. Her shockwave-punches are enough to make sure he never lays a hand on her anyway, then a mega punch puts him down.