Yeah I made it to the end and could of used a bit more powering up. But I found Water to be a strong spell for damage as an alternative for Ultima (which I did since my Ultima's were junctioned to Squalls HP so yeah I couldn't really use that too effectively.) If you have Eden you could use it to help take you through the first 2 forms or so really fast, just remember to boost up a lot. Also if I'm not mistaken every form final boss in VIII absorbs Holy. If you have Aura you could use it to get out some nice Limits for damage for a bit.

Really though in the end for me I just Edened my way through the GF portion and then hack and slashed, casted a few spells, and just slowly ate away her HP for well over an hour before I managed to win eventually.