The woman refused to listen when her daughter pleaded for help for fear that her husband would end their relationship, the court heard.
The man was described in court as an evil and wicked step-father and was jailed for 20 years after a jury convicted him of impregnating his step-daughter.
He began sexually assaulting his victim when she was aged 10 years while they were on holiday and then continuously raped and sexually assaulted his victim in her own home until she was 16 years old.
Prosecuting counsel, Angus Robertson, described an incident where the step-father raped the young girl while they were in the living room watching football on TV and the mother shouted downstairs to ask what they were doing. The step-father had shouted back ‘nothing’, and no more was said - but the girl maintained in court the mother had known.
Mr Robertson said the girl discovered she was pregnant was she was not even a teenager.
“She had a termination of the pregnancy. She did not want to have that termination,” he said.
He added: “She became pregnant again when she was a teenager, told her mother the father was the first defendant and said they could have her child. Both defendants were attempting to have a child of their own. Her mother considered this, but told her to ‘get rid of it’.”
The mother burst into tears as she received her sentence for neglect.
Judge Francis Sheridan told her: “The tears you shed are for yourself. I do not think any of them are for your daughter. I am not in any way influenced. You have not shown any sign of remorse."
He added: “It is time somebody told you to your face - and I will: You were a wicked mother. When your daughter complained, her complaints were dismissed. You will take that dismissal to the grave. You betrayed your daughter to stand by your husband.
“She has gone through what can only be described as a life of hell. There must have been times in her young life where there appeared to be almost no remission from abuse.”
To the stepdad, who kept his head bowed throughout, Judge Sheridan said: “You were a thoroughly evil and wicked stepfather. Let’s call it exactly what it is."
He added: “The jury believed your step-daughter. That is her first step to recovery from a life of hell inflicted by you, with the sex drive of a monster.
“You treated your step-daughter as an object. If you wanted sexual contact, she had to deliver and the poor little thing was scared to say anything and when she did, her complaints were dismissed. A little girl, an innocent little girl, corrupted and for those years whilst under your care, her life was ruined.”
The court heard the abuse began at the family home in in Milton Keynes in April 2003, when the girl was just 12 years old. It continued for four years because the mum refused to believe her daughter and took no steps to protect her for the next four years.
It was only years later that the girl found the courage to complain to police but her mother and step-father denied all the charges brought against them.
The court heard she now wants no contact with her mum.
"She wants you out of her life," said judge Sheridan.
He sentenced her to three years imprisonment. This will be in force indefinitely.