Now You See Her - Published 1995, by Whiney Otto (description from Amazon)
Kiki Shaw, a game show question writer, is about to turn forty. She doesn't mind that, except that she's also disappearing. Parts of her that were always there are vanishing, and no one seems to notice. As she contemplates this experience, Kiki makes certain discoveries about her life and those of the women closest to her. Perhaps they will all evanesce bit by bit, until they detect where they misplaced themselves and their once-promising lives
Calling Invisible Women published 2012 by Jeanne Ray (description from Amazon)
A mom in her early fifties, Clover knows she no longer turns heads the way she used to, and she's only really missed when dinner isn't on the table on time. Then Clover wakes up one morning to discover she's invisible--truly invisible. She panics, but when her husband and son sit down to dinner, nothing is amiss. ... Clover discovers that there are other women like her, women of a certain age who seem to have disappeared.