Amethyst Heart by Penelope J. Stokes

When she discovers her son has designs to sell her home out from under her, Miss Amethyst-ninety-three years old and as sharp as ever-isn't about to let her legacy go. She pins her hopes on her granddaughter, Little Am, a good-natured child who has mutated in her teenage years into something else altogether. Whatever it takes, Little Am will know that the Noble family heritage is worth fighting for.