[quote:f957893f29="Hsing"]And Agnes... I suppose she was to fill the gap Magrat left. I -again- seem to remember Nanny Ogg and Mistress Weatherwax talking about the fact that Magrat was now busy Queening and all, plus being a mother. (It was more the Queening, though, it seems, being a mother didn't stop Nanny after all.)[/quote:f957893f29]

In a witches coven there's The Maiden, The Mother and [size=9:f957893f29]the Crone[/size:f957893f29].
With Magrat now being a "Mother", and Nanny not willing to give up her spot, they needed a new "Maiden", so they recruited Agnes/Perdita X.

Of course Granny is technically a Maiden and will never be "The other one", so Agnes is never named as the Maiden.
Just remember that Nanny and Granny can bend the rules as they see fit and need someone to push around.


Edit: Spling