While she's long dead by the time of The Dispossessed, her existence and her philosophy are very relevant to that book and frequently mentioned within it.

At which point I'd be happy to call it continuity of culture rather than character anyway. But when I write a more polished version of this for my site, I'm planning to note how much of a fuzzy gradient there is between the Platonic ideal of a Setting Series and series where characters from one story appear in another, in varying degrees up to the romance model I mentioned here.