Love/hate relationships between sisters in childhood may continue unresolved, affecting self-image and adult relationships--so says journalist Mathias (The Washington Post, Family Circle, etc.), who here offers shallow exploration as well as gushy encouragement for estranged sisters to reconnect. ""Our parents die, our children leave, we can separate from our husbands or lovers, but a sister remains part of us...."" Sisters, Mathias says, are not bonded by genetics or--because each sister experiences the family in a different way--even by shared history, but rather ""by their gender, which is trained from early childhood to be sensitive to others."" Mathias's observations, based on interviews with more than 75 women, are intended to encourage therapists to consider more than birth order in evaluating the influence of the sister relationship and to encourage sisters to get past lifelong grievances and to reaffirm their loving connection. The author finds that sisters can be too close or too emotionally distant. Women are more likely to confide intimate matters to friends than to sisters, but when a woman is in a crisis (especially medical), her sister (regardless of past tension) will almost always be a first support. Unresolved resentments and jealousies from childhood will complicate other crises, especially involving the care of ailing parents. Mathias's prose badly needs editing (e.g., two sisters ""had already gleaned and dedicated themselves to two opposing passions of interest"") and her discussion ranges from the fairly obvious to the questionable--but sisters troubled by conflicted relationships will at least learn that that's par for the course.