Mother Dowson is a very minor priestess of the Goddess Asheth whom we hear about from the Goddess when she is explaining why the statue of the goddess in the temple doesn't appear (to Christopher) to be the sharpest tool in the temple. "Oh, that's just her very stupid expression," the Goddess tells Christopher. "It's very useful. I use it myself when Mother Proudfoot or Mother Dowson goes boring on."
So we don't know much about her, but evidently she can be quite, quite boring.