Since Schala is thought to be one of the ones orchestrating the events of Chrono Cross, and since she is in the Tesseract, she has access to every timeline, every dimension.
One could argue that Chrono Trigger and Chrono Cross happen simultaneously. If that's true, then Schala is able to change events in both adventures.
I don't think Schala is the entity, but that's just my way of trying to explain the notion.
Actually, it is not Schala, but Belthesar that is thought to be, and proven to be, orchestrating the events. The only aid she lends is the creation of her clone during the famed storm that swept Serge to Chronopolis in his youth. Other than this, the only other influences she has is in that she rescues Serge in his youth, splitting the dimensions: but she does this from a future time, presumably after she was saved, and acting in accordance with Belthesar. So he is the one orchestrating it, yet is not the Entity.
The thing is, the Entity is the planet, short and simple. Personally, I would like it to be God, but that, I know full well, is not the intent. When the Entity is first mentioned (and is this not the only time?) in the forest of south Zenan, it is mentioned that all these things, these time periods, that they saw, were perhaps the death-sights of a dying Entity, like the life flashing before one's eyes. Now, Schala had nothing to do with 65mil BC, so that rules her out. In fact, it rules out everyone but the Planet and Lavos. Presumably, Lavos would not orchestrate his own destruction. Thus this leaves only the Planet which, I must point out, ties in with the very apparent overall theme of environmentalism, shown once again in the end of CC. There is speaks of all things on this world being a dream of the Planet. Thus the Planet is what it all revolves around. Seriously, as much as I've wished to believe otherwise, I can see no other true explanation.
