Working out Qualifying NI years for State Pension

Hi - I am trying to work out if my mum is getting paid the correct amount for her basic State Pension. She was born in 1946, started to receive her basic state pension in 2006. Her online national insurance record shows she has 20 years full year contributions. We have spoken with HMRC and they have confirmed she has 25 years HRP between 1978 and 2003. Her full year contributions through employment dates are: 5 years before 1975 (before HRP eligible years) 12 years within "HRP eligible years" 1978-2003 3 years after HRP eligible dates (2003-2006) As I understand it, she would require 39 years qualifying NI contributions to be entitled to a full state pension (£156.20 per week). The HRP grant years would be 13 years (as she worked for 12 of these years). This would reduce her qualifying years for full pension down to 26 years. So is she entitled to 20 out of 26 years (£120.15) or 33 out of 39 years for her pension (£132.17)? Thanks to anyone who could help!

Hi Macd909,
As your mum is over State Pension Age, The Pension Service will be able to check that they have calculated her pension correctly and that they have included her periods of Home Responsibilities Protection (HRP).  
Their telephone number is 0800 731 0469.  
Your mum should be with you when you call so that she can pass their security questions.
Thank you.