Tightrope — Gillian Cross

Ashley's life is different from other teenagers. She has to look after her disabled mother full-time and take care of the house. She copes by being relentlessly cheerful and confident. But Ashley has a secret alter-ego: the dare-devil graffiti artist who has been tagging walls. And she has
an admirer in the form of Eddie, a local gang boss. Before long, Ashley is sucked into his world and into a sinister plan to destroy the life of a local shopkeeper. Almost reduced to despair, Ashley turns to her mother for help. Together they devise a way to defeat Eddie and at the same time develop
a stronger and better relationship.