I'd normally say that such a boss would be a hard boss, but she's actually moderately easy, well, if you count out the mega death attack she uses in what I think is her final form!
Argh, it's plain ridiculous. It sometimes casts death on all the members of my party (which in this particular battle, usually consists of Rikku, Auron and Yuna) and I practically have no chance! It's ridiculous. And before you tell me to equip armour that prevents death, that also cuts down strength, magic, and MP. Bah..
Oh, and before you ask, I've only just managed to play FFX, due to the previous lack of a PS2.