That's where it gets murky, and I think the anime made it even more so since Celia basically looks like a grown-up version of Pacifica there, as opposed to novel!Celia. So I think only part of her DNA was used (if any of it was, I really should check the source before running my mouth, BUT ANYWAY), just enough that she can nullify the Peacemakers' abilities and trigger the Guardian genes in Shannon and Raquel. The rest seems to have come from Elmire, particularly the bits that account for her (and Forsyth's) appearance.

All of this is enough to make a geneticist vomit blood, I'm sure.