I didn't get holy till long after yunalesca, it wasn't horrible without it, but it's handy when you do have it, because you can have Lulu learn it (if lulu has learned doublecast even better)and Rikku use copycat, so you'll get 3, maybe 4 holy's off. I whacked heck out of her, used everybody in overdrive and then then cast one Aeon per form in overdrive (except for her last form I cast 2 Aeons). I I left Bahamut for her last form in overdrive and then I used shiva I think. You can get them in overdrive beforehand and keep Yuna out of it so you don't have to wait until her turn, you can bring her in as you want her. After Yunalesca's first form I left everyone in Zombie and cast life as they died. Good luck, you'll get there!