Claudia Kincaid is the main character in E.L. Konigsburg's From the Mixed-Up Files of Mrs. Basil E. Frankweiler, and she is not being appreciated by her family--or at least that is how she feels. Once the twelve-year-old purposes to run away, she realizes she does not have the resources (money) to do so alone. She has plenty of family to choose from, but she selects her nine-year-old brother Jamie as her partner.
It turns out he is the best choice, for he has the resources she needs (money) to put her plan in motion. It is Jamie's $24.43 and her discovery of an unpunched train ticket in a trash can which allow her to, as you say, "launch her plan sooner than she expected."