here's the Rub, Hamburger, if she knows about needing to cast Holy, she knows about Sephiroth's need for Meteor.
you could.. just fucking stop the Meteor handoff, mind you, her casting Holy doesn't stop Meteor and only lessens the effects, likely the planet gets wrecked by Meteor+holy hitting it and many many people die.. so I dunno, altering the timeline so Meteor never gets cast is likely a way better plan than just doing the same shit again.
also she could just fling herself into the Lifestream to cast Holy, it doesn't require her death, its an actual fucking physical place you can fall into.
and despite my bitching, there is a very good bittersweet angle with the remakes they lay out, Aerith knows she's going to die, knows this adventure is the last she'll have, and these are the only true friends she'll ever make, and that she will never have the love of Zack or Cloud and its perfectly encapsulated in this song.
https://youtube.com/watch?v=uZr337zWYVY, list: RDuZr337zWYVY
She knows the "day" they meet again is solely when they all meet in the afterlife/lifestream, its all very tragic but its sad that it has to happen for no reason.