In the novel Sleeping Murder, Mrs Saunders was a former cook of Colonel and Mrs Bantry. After she and her husband were left a legacy by a former employer, they left service and set up a boardinghouse at 14 Sea Parade Dillmouth.
When Miss Marple planned to visit Dillmouth, she thought of staying with them. Mrs Bantry thought it was a good idea as she was a good cook and would look after Miss Marple well. Mrs Bantry called her "The Mock Turtle". She was a "Woman with a deep mournful voice who always sounded as though she was going to burst into tears".
The Saunders are not mentioned by name in the BBC 1987 adaptation of the novel, but while in Dillmouth, Miss Marple does stay with "a friend's former cook" who takes boarders. This matches the description of Mrs Saunders.