Gwen Van Dam, a Character Actress for 70 Years, Dies at 96 (https://www.hollywoodreporter.com/movies/movie-news/gwen-van-dam-dead-character-actress-1236099247/)
The article doesn't list DS, but she played a secretary at the Foundling Home in Episode 8. Robin's summary of her scene is below (sometimes her boss was a Miss, sometimes a Mrs.) with MB's capture of her on the left:
Miss Hopewell orders her secretary to send this letter to Miss Victoria Winters, Collinswood, Collinsport, Maine--"Dear Victoria--I think you should know that shortly after our telephone conversation today, I received a visit from a man who said that he was a magazine writer, and finally admitted he was a private detective--oddly enough, his inquiry was almost the same as our phone conversation(http://www.dsboards.com/epimgs/0008-5.jpg)
--he was anxious to learn why you had been hired by the Collins family, who recommended you, and the rest of it--the detective's name was Wilbur Strake--do you know this man, or have you any idea who hired him to learn this facts about you?"
With thanks to Kosmo!