A touching novel about girls and their mothers, sibling rivalry and kinship, and the mysterious tug between love and antagonism that lies at the heart of every family.     The year Tilden turns twelve, her mother, Frances, falls in love and moves the family north.  Soon the watchful, wise Tilden and her rebellious younger sister, Elizabeth, are navigating a new household amidst the awkward and alluring terrain of adolescence.  But when Frances suddenly discovers a lump in her breast, her daughters must confront the unpredictablility of her illness.  With heartbreak and humor, these characters exposes a world of secrets and learn to survive in the face of life's contradictions.     This moving, emotionally stirring debut novel will appeal to fans of Anna Quidlen's One True Thing and Mona Simpson's Anywhere But Here. Funny, haunting, and unflinchingly truthful on every page, What Girls Learn is a book that will be read--and cherished-- for years to come.