Aeris isn't selfish enough to wish it undone; it was necessary for a Cetra soul to carry Holy's plea into the Lifestream, and to wish it undone would also be to wish everything and everyone dead. But she still had things she wished to do, friends she left behind. She might watch over them from in here, but it's not the same. She is selfish enough to wish it might have been done differently, and doesn't think there's anything particularly wrong in that.
But it does seem short-sighted, especially as it becomes clear that Jenova has not finished toying with those she infected, and there is still a lot of work to be done in restoring the Planet to what it was. Holy's plea was carried by the last Cetra soul still amongst the living; what if it is needed again? Who will call it forth?
Perhaps the other Cetra are content to dwell within their Promised Land, but the land that concerns Aeris is more substantial and less perfect than that.
It is possible. Sephiroth's repeated resurrections prove that, even if the reason the Lifestream let him go was because the Jenova cells still had too firm a grip on him to allow him to be absorbed. Finally, her arguments bear fruit, and she finds herself breaking the surface of the water just off the coast of Mideel where blue ocean and green Lifestream mingle in dazzling aqua shades. She sucks in the first breath of real air that she's breathed in years, tasting the salt on her lips. The blue sky above is almost blinding in its brilliance, and the shrill cries of the gulls that circle above hit her ears almost like an assault before settling to a more normal volume.
Then she feels the sea beside her shifting in something that is not the rhythmic rise and fall of the waves. A black-haired head breaks the surface, spluttering as it shakes wet spikes free of water. She laughs in delight as Zack turns to her with a familiar grin, and offers to race her to the shore.
"Only if I get a decent head start, SOLDIER boy," she retorts, pointing out that really, he does have a totally unfair advantage over her. "Count to at least a hundred, and no skipping numbers." She sets off before he can object, because it's not that far and by the time he reaches one hundred, she might already be on dry land.
Zack's return makes her think that just maybe the Cetra saw right through her all her carefully reasoned pleas and arguments, but she doesn't care. Life is too short to waste on worrying about minor details, after all.