If indeed actress Sarah Churchill was Leslie Howard's assistant then she would know Laurence Olivier who was the husband of Viven Leigh.
Of course David O Selznick from Pittsburgh produce the movie Gone With the Wind.The reason David O Selznick was from Pittsburgh is because his father Louis Selznick worked for Warner Brothers Studio located in the old Bakewell Glass building in Pittsburgh in the early 1900's.
James O'Hara was business partners with Benjamin Bakewell who's name was on the building.James O'Hara's granddaughter, Mary Croghan O'Hara, married William Schenley.William Schenley was a Royal Guard to Queen Victoria.She met him when she visited Queen Victoria for the summer. A very well recorded event.
William Croghan, her father, was well recorded to be connected to both the Churchills, Bakewells and Clarks of Kentucky. He was a nephew of George Croghan who was connected to James Fenimore Cooper's father William Cooper the Mayor of Albany.
So again I think the Churchills of Kentucky, Pittsburgh and Rochester are related.