Greenie knew Persephone, yes, but it's not necessarily Nerwen.
Also, an interesting quesion. Since Demeter's place was to protect Persephone, doesn't that in a way make her evil? Kind of like the cobbler's secretary or something? And if so, why would she be hinting at Persephone's identity?
Either way, really, I'm not sure I buy this.
More thoughts in a moment, but first dinner.