I thought the return beads cannot be used until she's defeated? But now it's essentially, "Her negative influence is gone if Jin brings her back with him by returning to his world." So that's kind of a circular problem... How do they plan to return without the return beads?
Also, I have to seriously question the name being rendered as "John" in the translation, since it's firmly in the realm of being a masculine name and, perhaps more important, the raw has it written as ヨーン ( Yōn ).
So then what are some other alternatives for ヨーン?
Jørn, Joen (although those two are — like John — also masculine) or Yong.
If I were translating, I would probably choose
Yong (용).
I don't know for certain that she's a dragon, but it would make sense if she were to be a type of dragon, given how the Greed Zeld'don was a dragon, how she instantly recognized Ryu as a dragon disguised as a human, and given her own physical features (which, to be fair resemble a devil's more than a dragon's). A Korean dragon does have horns, although it seems they often
more closely resemble antlers.
Of course, I could easily be wrong, about a lot of things, but it still doesn't sit well with me to see a girl character named John. Without knowing the author's intentions, there's no way to know with certainty the correct way to render her name in English.