Don't read the below if you don't like spoilers.
Farm a bunch of torpedoes in the airship, get some plot holes from the castle (5+ is ideal), and level up a half decent combat familiar - I tried my new MicroMechaMech last time and that thing did a heap of damage, but any combat familiar will help as long as it's a decent level. Get its item from the arena too, of course.
Then lose to her 10 times in a row on purpose, get 30 homeopathic elixirs in case you need them, and put on the furry suit and any +hp/mana items you have (but no +stats) and of course the wand. If you have them, flaming talons are nice for the offhand. Oh yeah, and since you're a DB, make sure you have the skill that lets you use two items per round, I forget what it's called, as that will greatly increase your odds. Another good thing to have is the chronic indigestion skill you get for eating an insanely spice enchanted bean burrito, so cook and eat one of those if you haven't already.
Ok, so why lose to her so many times? It makes her interrupt your item and skill uses less. Much less, if you lose a lot. So your tactic will be to rely on items/skills to do most of the work, plot holes to delevel her a bit to make her miss more, and torpedoes and chonic indigestion to really hurt her. And it will also let you get those healing potions through most of the time when you need them instead of seeing them wasted time after time.
On the first form, use two plot holes and then torpedo/chronic indigestion her down. If you don't have so many torpedoes and/or mana, use some normal attacks with the wand as well as this will always let your familiar act and hopefully do some damage even if you miss, and if you do hit the talons will make sure you at least make a dent. If you get below 80% health, use a healing potion, as you want to be near full health once the first form dies.
On the second form, it's the same deal, just use 3 plot holes instead of two as this one will let itself be deleveled a bit more before dispelling it. Also, you can let yourself get somewhat more damaged as you won't need any health for the 3rd fight as long as you can get there, so just use enough to stay alive and otherwise concentrate on damage. This form does more damage though so don't let yourself drop too far.
If you get past this form, just watch the show.