G.P letter for appeal

I was hoping for some advice please. My wife was transferred from DLA to PiP and although she was awarded Higher Care she was only awarded Lower mobility, the reasons they gave for awarding the lower points were very vague and although i keep applying for the assessors report and have requested it 4 times since her assessment on 17th April I still have not received it to date. I put in a M.R. on the points i did not agree with and they have refused the M.R. I am now considering appealing the award and i have an appointment to see our G.P. so my question is What do i need to ask the G.P to write in the letter, should it just cover the mobility descriptors or the whole award? She refuses to see anyone else due to her mental health issues so we have no further evidence to support the claim.

Thank you Gordon I will check the guides and the form we filled in before i see him.