In the book Sarah's Key, is Mamé the mother of Bertrand?
Sarah's Key is a historical novel by Tatiana de Rosnay, published in 2006, about the French Vel' d'Hiv Roundup that took many Jews to concentration camps in 1942. The story concerns a young girl -- Sarah -- who is taken in the Roundup, and the modern-day journalist who becomes fascinated with Sarah's story.
Julia, the journalist, is married to Bertrand, whose family lived in the area during the time of the Roundup. She begins to question his family who still live in the area, much to his displeasure. One person she speaks with is Mamé, Bertrand's Grandmother, who is suffering from dementia.
"Don't call her [Julia] Madame Tézac," barked Bertrand's grandmother. "She hates it... anyway, Madame Tézac, that's me, said the old lady with a touch of haughtiness, and total disdain for the other Madame Tézac, her daughter-in-law Colette, Bertrand's mother. So typical of Mamé, I thought...
(de Rosnay, Sarah's Key, Google Books)
The paragraph makes it clear that Mamé is Bertrand's grandmother, and Colette is his mother. Colette appears in the novel, but Mamé plays a much larger role.