The soap matriarch, who passed away aged 65 in February after losing her battle with cancer, plays a cook who gets mixed up in a murder case.
Wendy filmed the scenes, which will appear in the adapted for ITV version of Agatha Christie story A Pocket Full Of Rye last year. Cranford actress Julia McKenzie debuts as the female sleuth, taking over from Geraldine McEwan.
"For everybody who loved Wendy, watching Miss Marple will be an emotional experience," says a source from the channel.
"It has the blessing of her beloved husband John Burns and the rest of her friends and family."