There was a rumour a little while ago (like ten years ago!) that stated that Square were in a rush to finish the game to make the deadline, and though they had been planning a resurrection of Aeris, they couldn't finish this part of the game. This 'explains' why, if you use a Gameshark or other game hacking equipment and play, for instance, the part after the snowboarding, she has, or appears to have, her own unique dialogue. This rumour was even in a couple of Playstation magazines

However, this rumour was later refuted by the person who began it in the first place, claiming it had all been a bit of a joke.

There is, however, a 'ghost' of Aeris in the church, though this has been confirmed as a glitch.

Lots of evidence to the contrary has proved that they never planned nor meant to resurrect Aeris.