Brat

On her twelfth birthday Brat's father disappears. She waits, but he never comes back. When she goes looking she is laughed at, and her belongings stolen. Reduced to begging and determined to find out what has happened to him, she falls in with Gray and Baylock, whom she quickly discovers are outlaws, but there is far more to either of them than a falling out with the law, and Brat find that nothing is simple, nowhere is safe, and being reunited with her family is going to be difficult, and something she may decide must wait as more pressing tasks fall into her path.
Ghillian Potts is now 83. She had a number of stories for younger children published in the 1990s, one of which featured on Jackanory. Young adult novels have been written at various stages in her career, but none have been published until now.