In the game, she succeeded in casting it before her death. The reason there’s another disk is Sephiroth is preventing it from working. So Cloud et al go deal with him, then holy happens, end of game. If she survives, not much changes at that level.
The combat felt really slow to me, but I continued for a while until the game soft locked by just putting the characters in a small, black room. Nothing I could find fixed that and there wasn’t enough of a draw to really look for a fix. Might try again at some point but it was only so so for me overall.