Name the actress that played...
...Aunt Effie, Effie Ramsbottom I believe. The character and actress aren't listed here on IMDB, nor in the episode credits at the end of the show.
shareFor some reason they changed the character's surname (not the only time in this series). Aunt Effie is "Miss Henderson" and the actress was the late great Fabia Drake. It was a shame she didn't appear in more scenes as the adapter could have made more of her. In the book she suspected who the murderer was but was fond of him/her (not to give it away) despite her religious extremism. However, she has the best line in the adaptation which she delivers with gusto:
Adele (to her lover): "...I'll see you in the clubhouse
Aunt Effie (overhearing): "Clubhouse ? WHOREhouse....!!"