Maybe in the context of the novel you are reading, "mother" has become negative? Without reading it, it's difficult to say! However "mother" is part of a very strong profanity, and if you say "You mother...." to someone, the entire profanity is implied.
It is possible that in some cultures, an old woman could be called "mother" whether she is or is not your biological mother. It could be a sign of respect?
(not a teacher)
- For Teachers