With more people living into their 80's and 90's, these women are finding that the responsibility of caring for a frail parent or parent-in-law can last more than a decade. While some men provide the primary care to their parents, the usual pattern is that sons offer financial help while daughters or daughters-in-law do the hands-on care. ''And it's going to be primarily women for a long time,'' said Elaine -- ''With many more very old people, and fewer children per family, almost every woman is going to have to take care of an aging parent or parent-in-law,'' she said. To do that, many switch to part-time jobs, pass up promotions or quit