NBC / NBCUniversal via Getty Images Sitcom actress Melanie Watson Bernhardt has died at the age of 57. According to her brother, Watson died on Friday in Colorado Springs. Watson, who was born with osteogenesis imperfecta—commonly known as brittle bone disease—had reportedly been admitted to hospital with bleeding issues before her passing. Her brother, Robert Watson, added that doctors did their best to help her, but that she was “fortunate” to live for her 57 years. Watson played Arnie’s friend Kathy Gordon on ‘Diff’rent Strokes.’ She guest-starred in one episode per season from 1980 to 1984. In 1982, there was an episode named after Watson’s character, titled “Kathy.” After leaving the sitcom, Watson went on to help others living with disabilities. According to her IMDb profile , Watson was a founder and executive at Train Rite, an organization that trains dogs to help people with disabilities. Read more at The Daily Beast.