If "Mummy" did not want sex, then she was raped.
That isn't true. If Mummy didn't want sex and said so and Daddy ignored her, she was raped.
If Daddy said, "How about some?" and Mummy wasn't really in the mood but thought fine, whatever, and said "Oh, all right then", then she wasn't raped.
It implies she didn't want a child, which is still a pretty horrible thing to find when you're looking through your baby photos in ten years time.