Never heard of her, but I found this interesting.
Joan Washington, Dialect Coach to the Stars, Dies at 74
In a career spanning four decades, Ms. Washington developed a reputation as a sort of reverse version of Henry Higgins, the elocutionist who taught Eliza Doolittle the King’s English in George Bernard Shaw’s play “Pygmalion”: She instructed actors to speak not just in national dialects but also in regional and local lilts, even historical ones.
risingbulletin.com/joan-washington-dialect-coach-to-the-stars-dies-at-74/