I doubt if Goodie's small library contained any grimoires: not a witch thing, especially such a practical research witch as Mistress Whemper. More likely medicine, pharmacy and natural science texts, some likely written by herself.--Old Dickens 23:26, 19 May 2007 (CEST)
Just checked the reference. Wyrd Sisters, p51 (Corgi paperback).
Magrat appears to admit to Granny that she's been reading again....
Granny Weatherwax:- "And you bin reading them funny books. Grimmers."
Magrat Garlick:- "Grimoires-"
I could accept that the sort of "grimoire" a person like Magrat might acquire could have C.M.O.T. Dibbler on the publisher's credits page, though... although even Dibbler might think twice about marketing an almost-grimoire from his "offices" in Sator Square, right under the noses of the Wizards.... perhaps Mistress Whemper acquired a couple as part of her researches, even if it might be something as innoccuous as Woddeley's Occult Primer?--AgProv 23:39, 19 May 2007 (CEST)
Since she was mostly engaged in finding which ingredients worked best in the vaguely-worded old recipes, I suppose she may have had some texts on which to base her research, although other witches were unlikely to write them down. More probably, as you say, grimoires would be Magrat's, and likely of the Dibbler type.--Old Dickens 23:54, 19 May 2007 (CEST)