Она действительно убила оригинального Серого Мальчика. Не помню были ли это в тексте, но в Слове Автора прямо говорится:
Cauldron permitted Gray Boy because he was the closest thing to a weapon they had against Scion since Eidolon. When the S9 started picking up and more parahumans started getting removed from the fiend than Gray Boy was theoretically worth, they moved in. Manuevering Glaistig Uaine into taking him over, so the power would still be in play.