The second time I faced Josephine, which was in the Black Ring Phase, I ran straight at her with my "Sword of the Gods" and hit her before she could cast magic. It froze her and made simple work of the task.
The first time I went after her I used deadly discs and some fancy footwork and summoned some diversions to face her.
Josephine was easily the toughest character in the game.
Good Luck!
