Emeralda was created by Kim Kasim during the Zeboim era, four thousand years before the beginning of Xenogears. She is a nanomachine colony created to resemble both Kim and Elly, probably in an attempt to make her their 'real' child, although she never had the chance to awaken and fulfill that role. She was also Kim's attempt to create a perfect human being in a time when humanity was steadily destroying itself with radiation poisoning and all-out war - a wish come true for Kim and Elly, who could not have children because of those circumstances.
Clothing size: medium
Shoe size: 20/23
Ring size: 6/8
Even though Emeralda never woke up (according to various translations of the PW on the boards), she seems to know Kim. It's possible he spoke to her while she slept, or maybe planted information and images in her mind so she would know how to act when she was finally released from the nanoreactor. But she doesn't know Elly, and that is strange. ^.^ Her reaction to Fei is funny, though. "Fei's Kim! Fei's Kim!"
When Emeralda does finally wake up, four thousand years later, it is to be nabbed by Tolone and Seraphita and taken to Solaris for Krelian to experiment on. There are no details of her time in his lab, but when she is released with Crescens, she is ordered to confront Fei and his friends, and she falls into their hands.
The rest can be learned by playing the game, or picking through the Episode Three summary. For such a complex character, there's remarkably little to say about her history.