Obito's Genjutsu can overwhelm Katsuyu as it did the Kyuubi back when he was fourteen years old.
As for Tsunade herself, he can spam his Juubi sized Katons at her, effectively roasting her and forcing her to heal until she runs out of chakra. Or, if he wants to play it risky, he can approach her in CQC with one of those big shurikens of his and use Sharingan precognition to dodge her strikes and then proceed to decapitate her. He can also Genjutsu Tsunade to make CQC even safer.