I just started Witches Abroad
. It seems Magrat is Terry's way of making an interesting point, that self actualization is not achieved through self absorption. Despite the fact that she is best learned and most intelligent of the trio, she is also the greatest idiot (as far as I have got) because there is too much "me me me" in her makeup.
Anyway, it seems that Magrat makes her greatest progress in makeing a better personality for herself when she is doing for others.
A Terry Heroine is kind of startling in literary terms because she never looks for rescue. Not that she isn't in tough places now and then. A Terry Heroine is never one who relies on anybody, but is instead someone everybody can rely on. Susan, Tiffany and Polly are very similar in this regard.
I think, by drawing a line between Susan and Magrat, we can get a pretty good understanding of what Lynn Practchett is like.
It would be a mistake to think that they weren't also dangerous, just because reading them didn't make fireworks go off in the sky. Reading them sometimes did the more dangerous trick of making fireworks go off in the privacy of the reader's brain.