In the novel Postern of Fate, Gwenda is a friend of Beatrice, the Beresford maid. Gwenda works at the post office shop in Hollowquay known as Mrs Garrison's and manages the side of the shop that sells postcards, stationery and sundry items.
Beatrice mentioned that Gwenda had heard that Tuppence was interested in information about Mary Jordan and she thought she might know something. Gwenda turned out to be a useful resource person. Her information came from what her grandmother told her and a bit from an old gardener Isaac Bodlicott. Mary Jordan was a German governess or au pair girl but Gwenda's grandmother thought she was a German spy. Mary Jordan had been with a naval family up north in Scotland and then came to live with the Parkinsons who used to own Swallow's Nest. She died after an incident when someone mistakenly brought foxglove leaves into the kitchen thinking it was spinach. Mary Jordan also used to paint pictures. She painted one of Gwenda's great aunt Aunt Fanny, and another one of Alexander Parkinson who, according to Gwenda, had died young and was a godson of Mrs Griffin.