The episode was filmed as part of Series 3, but is being held until the festive period before it is broadcast.
She confirmed: "There is a Christmas special. The icing on the Christmas cake is a very special appearance by one of my ultimate comedy heroes, Jennifer Saunders. She may play my mother, yes."
Elaborating further about the role, Howe-Douglas explained: "We wrote the part for her; we wrote it with her in mind, but kind of going 'would she do it?'... she's been very supportive of us on t'internet.
"She was just so kind when she came in, about the show, and I said to her 'thank you so much Jennifer for doing this' and she was like 'Well how could I not? It's just about the best thing on television'. I was like '[gasp] I used to watch you as a child!'
"You know sometimes don't meet your heroes - mention no names - but, yeah, she was no disappointment to me."
Talking about acting alongside the French & Saunders star, Howe-Douglas added: "Her kind of depiction of what Fanny's mum would be like had elements of Fanny Button in it - it's such a strange thing to have your comedy hero do a little bit of what you do, but in their own incredible way."
The special will be shown on BBC One this December.
Series 4 of Ghosts has yet to be confirmed by the BBC, but a recommission is expected. When asked if there will be another series of the show, Howe-Douglas said: "Well, there may be one in the offing. We very much hope so, but I'm not allowed to say anything at the moment."
The American re-make of Ghosts (trailer) recently started on the CBS network, with UK creators Mathew Baynton, Simon Farnaby, Jim Howick, Martha Howe-Douglas, Laurence Rickard and Ben Willbond acting as executive producers on the project. The series - which stars Rose McIver and Utkarsh Ambudkar - has met with good reviews. The Wall Street Journal said: "There are certainly no shows on TV more spirited than Ghosts right now and there may be none funnier."