An easy and cheap way is to do the following:

Get on the dragon's back and start performing Strike Raid repeatedly until she dies. Yes, this requires a lot of MP but you are out of harms way for most of the fight (she'll knock you off from time to time).

But, yeah summon Tinkerbell, use Aero as much as possible, and hack away (if only you could have Ragnarok for this fight). If you are still having problems, equip Sora with stuff that increases his defense as much as possible, that should help quite a bit.