I didn't say that that was the only reason. We could also note that her parents were murdered and her mother-figure, Raine, died. We could note any number of reasons, or we could simply say that she's naturally quiet. It's not like it's a bad thing to be quiet, after all, and it doesn't make you inhuman. Heck, she even had a sense of humor, still.

And I don't think that Rinoa was routinely locked inside the house, nor do I think it really matters, even including that General Caraway was almost certainly not the only General.

The point is, there is absolutely no support for the idea that Ellone is a cyborg.

Now, to put it more on-topic, the idea of Irvine and Quistis being together was brought up by the original poster--it's kind of popular, and it actually does make sense, if Irvine can get over being...Well, Irvine. He and Quistis actually have some striking similarities.