Then, there's the modern mother-in-law. In her mid 40s, she is the compact car of her breed: efficient, trim, attractive and in harmony with her times. She's pretty stiff competition for the plain young matron who's overweight and under-financed. If there is going to be friction in this relationship, it could start from envy and resentment in the younger woman. But Father Time is on her side, even if Mother Nature played her a dirty trick