The Undertaking of Tess by Lesley Kagen

If she can't achieve her goals, she's desperately worried that her beautiful, but self-centered mother, Louise, might send emotionally fragile Birdie to the county insane asylum. Stronger and more down to earth than ethereal Birdie, Tess has always watched over her sister, so it's only natural for her to come up with a plan that she jots down on one of her never-ending to-do lists. Tessie needs to make sure that she does before their mom gets wind of how much "weirder" her sister s getting. Not only is she attempting to come to grips with the devastating loss and guilt she feels after witnessing her father's death, but her kid sister, Birdie, refuses to believe that their beloved daddy is really gone. During the summer of 1959, ten-year-old Theresa "Tessie" Finley has her work cut out for her.