The Amethyst Summer by Bianca Bradbury (1963)
All of these problems confronted Bayley because her mother had to leave her family one summer to take care of an ailing relative. Bayley rather lightly undertook to fill her place but almost immediately realized she was over her head. After a pretty grim start, however, she began to learn how to manage a house, serve an acceptable meal, and get her social life oriented toward dating rather than just being a good scout.
An excellent story for older girls, told with understanding and humor, about one of the most important facets of growing up. (from the inside flap)