Then She Found Me by Elinor Lipman
Given up for adoption thirty-six years ago, April Epner, now a quiet-living, sensible-jumper-wearing Latin teacher, has never had the slightest desire to be reunited with her biological mother. But, as it turns out, she doesn't have a choice. When Bernice Graverman, the brash, glamorous host of a mildly successful daytime TV talk show, flounces into her life claiming to be her mother, April is horrified: can she and this woman really share the same genes? Worse still, Bernice seems determined to take up her maternal role where she left off. Her first task: to tackle April's non-existent love life.