Olivia Gardner, a northern California teenager, was severely taunted and cyber-bullied by her classmates for more than two years. News of her bullying spread, eventually reaching two teenage girls from a neighboring town, sisters Emily and Sarah Buder. The girls were so moved by Olivia's story that they initiated a letter-writing campaign to help lift her spirits. It was a tender gesture of solidarity that set off an overwhelming chain reaction of support, encouragement, and love.

In Letters to a Bullied Girl, Olivia and the Buder sisters share an inspiring selection of...