I guess it depends why the results are lower than hoped. If she is not academic then she will not get hight results in academic exams and your DD should not be hassling her. There might be other things at which she will shine and be happy - or not - she may be someone who will not shine at anything in particular but lead a happy and productive life.
What was her attitude to the exams? How much do they matter to her?
My DGS did no homework at secondary school, but scraped enough GCSEs to get into college and is now at uni doing a degree in sound engineering - I am looking forward to seeing him on the credits of a Hollywood film!
I guess I must ask whether her high achiever Mum leads a relaxed and happy life! - some don't.
Changing from a Manual car to an Automatic after driving manual for around 50 yrs

