[UnderthethumbUK]

Hi, I am looking for a series of fantasy books that I originally read in the late 1980's, although they could have been published before that and I never finished the series, so the last books may have been published later! I cannot remember the author or titles, but I remember that the bad guys were intelligent monsters/beasts that each controlled a city. In one of the books, a female character, on the side of good, who has got near infinite magical powers travels through time/space and has a (I think) worm-like companion. That companion actually gets turned in to the main bad monster in the books. This has driven me crazy, on and off, for years. Any help would be greatly appreciated!