"There are a few possibilities, as I understand them...."
"The first is the traditional Sidhe way. If a suitable mortal vessel could be found, she could incarnate directly. It is effective, but it would mean displacing the mortal soul already there."
"The second is to entrust her to the Dreaming itself. There are tales of lost fae souls doing exactly that, surrendering themselves to the cycle and returning later as changelings born naturally into the world. It is a matter of faith, however. Once she enters the Dreaming, the path is no longer ours to guide."
"The third is what I believe may be possible with the urn. Not merely preserving her, but allowing her to change. A long sleep, of sorts. The vessel would become a chrysalis while she slowly adapts to the Autumn World. In time, she might become capable of entering the rebirth cycle naturally. And if Lady Nadeen is correct about the blood tie, there may be ways to anchor that rebirth to a specific mortal line or even a chosen mother, so that when she returns she is born to someone known to us rather than left entirely to chance. The Dreaming has always favored such stories."
He pauses, and says, "Lord Aiden may know more, he's far more knowledgable than I, or could even guide a scrying to find out more about this soul if possible."