Hi Boobam,
Have you started charming your items? In what difficulty setting are you playing? A lot of players here believe that Josephina is the toughest enemy in this game. I have to disagree. Well, may be she's the toughest compared to the rest, but she's not tough enough to beat you if you build your character right.
I don't have a specific strategy to offer. If you want one, you can try Raze's link. The only piece of advice I can give you is that try to have lots of hitpoints. This is the key to surviving her attacks. One of my characters, a mage, fought her when she was clvl 38. By then, she had 1200+ hitpoints and 1300+ mana. She could take a lot of Hellspikes. This is what I did: as soon as I got into her chamber, I was swarmed by the dwarves. I just stood still and kept atacking with Hellspikes until all the dwarves were dead. Josephina summoned a death knight, I let her. She attacked me with Hellspikes, I let her. If your character has enough hitpoints, he/she should be able to survive all the attacks. Just make sure you have enouh restoration potions in your inventory and hotkey them. The last thing I did: I froze her and attacked with Hellspikes. It took about 4 - 5 seconds until she gave up.
Of course, I only play in easy and normal modes. In hard mode, that's another story. Combat in DD is easy. The only difficulty that I found was solving some of the quests that involve puzzles (I'm not smart, I know <img src="/ubbthreads/images/graemlins/delight.gif" alt="" />).
Use large/very large charms that give health. You can buy them off vendors, especially in Ars Magicana. Some monsters drop charms when you kill them. Go hunt the orcs and the lizzards.