Marian is not in the Watson narrative, for the simple reason that she died ten years earlier. (This is not really a spoiler because one of the first statements Felix makes mentions that his mother is dead.) She is, however, very important to Felix’s story. There wasn’t really much involved in developing her character. Felix needed a mother who would teach him the things he needed to know, and so that was what Marian became. Her backstory, what little I know of it, rather intrigues me, though. Perhaps someday I’ll write about it.
Marian’s story is rather a hard luck story, but I’m sure she would not want to be pitied. She was not that kind of person. To find out more about Marian, read Across the Stars.