Very few have recorded the stress quotient in the young mother's sweaty world of Play Dob and leaking orifices with Thayer's punctilious attention, also displayed in her fresher first novel, Stepping (1980). However, beyond the romper room, this novel, about the self-liberation of two sisters and their mother, is a bit stiff with message. Daisy, 29, mother of two tots and expecting another in her beloved big house on Lake Michigan, is frightened: husband Paul, successful businessman and stinker, is leaving her for a thin, chic gal (Daisy's been spreading), and he insists that the house be sold. So distraught Daisy turns to mother Margaret, who was always the comforting Apple Pie Mom back in Iowa. But Margaret, now in Vancouver, has been through divorce, hair dye, weight loss, and--with lover Anthony and single blessedness by Vancouver's ocean--somehow old Mom is on a high which doesn't have much to do with maternal responsibility. Also puzzled by thoroughly modern Mom: Daisy's sister Dale, 24, a Maine high-school teacher who wonders about the value of marriage yet is ravaged by love for Hank, teacher and part-time farmer. (Dale is also disturbed by her adored father's self-pitying depression.) But then the lives of the three women pivot like a buoy at the change of tide. Margaret opts for a loving response to Daisy's need, really communicates with Dale, and, deciding not to pursue exhilarating change for its own sake, dumps Anthony and takes a job. Daisy finds women friends who give support (they gather in that obligatory feminist-fiction scene--the sisterly all-night group confessional); furthermore, after the birth of her daughter, Daisy achieves every mother's dream: a date with the obstetrician! And Dale, sozzled with requited passion for Hank, decides to take the marriage risk. Wading heavily but steadily into flashbacks and self-examinations, Thayer recycles son sturdy standbys: strong women at the mercy of, but breaking from, dependent men; the savage primacy of giving birth; equal partnership in sex; pal-ship motherhood. And though the characters tend to speechify at length, this is a sure thing for the Women's Room set--leisurely, hard-working, and softened a bit by nice scenic tributes to three pleasant locales.