In Equal Rites, then Arch-Chancellor Cutangle asks Granny Weatherwax if she would accept a Chair and give lectures on herbology and headology.
Is there evidence that she in fact did so in subsequent novels?
I'm going to say no.
That based on all adult Discworld books read to a point of dog-earedness, though admittedly not the Tiffany Achings ones, which I've only gone through once and didn't care for. Also included, the various guides and maps.
Maybe a deep search in the old Usenet archives, where Pterry used to post could turn up something.
Granny's only links seem to be a distant cousin, an old flame and a protegee!
Heck, we don't even hear of Eskarina ever again! EDIT: yes, we promptly do in the one I didn't finish I Shall Wear Midnight.
In Equal Rites, Granny Weatherwax puts forth a few good reasons not to lecture, and seems to reluctantly accede:
Granny frowned, and then nodded across the haze over the city to the distant glitter of the snow on the Ramtops. “It's a long way,” she said. “I can't be keeping on going backwards and forwards at my time of life.”
Perhaps most important, she merely resolves to "think about it," rather than actually agreeing:
“Practical things?” she said, thoughtfully.
“Absolutely,” said Cutangle.
“Mmph. Well, I'll think about it,” said Granny, dimly aware that one should never go too far on a first date.
I have read all the main Discworld books (though not Science of Discworld), and I do not recall any mention of Granny Weatherwax giving any lectures.
On the other hand, that does not mean it did not happen. It simply means it did not become so regular a part of Granny's life that it was still happening as of Lords and Ladies, for example.
The simplest explanation is that this is a different continuity than most other books follow - the existence of parallel realities is slightly hinted at in "Lords and Ladies", where Esme and Ridcully did barely not
spend their lives together.
Hex also sometimes seems to hint at this, and remember at the end of "Equal Rites", the most powerful form of magic turns out to be
yet in no future instalment you ever see a Wizard performing that art, let alone mastering it. There is also a strong chance that John Keel was not
replaced by Sam Vimes
before "Night Watch".
In summary, while this is probably not as complicated as the timelines in doctor-who, the explanation still boils down to this (attention, TVTropes link!):
"People assume that time is a strict progression of cause to effect, but actually — from a non-linear, non-subjective viewpoint — it's more like a big ball of wibbly-wobbly... timey-wimey... stuff."
— The Tenth Doctor, Doctor Who, "Blink"
And thus the answer is in "main" continuity, she didn't.