Morgan is the childhood playmate of Arthur and the only woman he'll ever love, etc. etc.  Nimue vaugely appears as the mother (with Merlin as the father) of Morgan. However, as a kind of not there character, she really doesn't do all that much while the fascinating character of Morgan does much more.  It's a decent book, but rather unmemorable in the vast swarm of Arthurian literature.

Dates:
The Road to Avalon: 1988