Claim cancelled for failure to attend medical

I have a client aged 62 (mental health problems and social isolation) who has been called for ESA medical assessments over the last year and has struggled to attend due to her mental health problems and has cancelled two appts. We have become involved to support her and discussed at length the need to go to the appt. She attended on 18.12.15 but was deemed unfit to examine as she got so upset that the HP was not qualified in mental health - he admitted this to her. She was then taken to a very small ante-room by two female members of staff who stood over her while she cried and tried to talk her into going back into the assessment room. In her words it was a very intimidating experience as the room was so small, she was already upset and they stood over her and got quite cross that she wouldn't go back in.
She came home, had problems getting off the train because of the gap to the platform, so made enquiries about the buses for the next appt. which she knew she would get.
On 16.1.16 she rang in distress as she had received a letter asking why she failed to attend an appt. on 14.1.16. By the time I saw her on 17.1.16 she had already written back stating that she did not receive an appt. letter for 14th Jan. I rang to tell DWP that she wanted Mandatory Reconsideration, explained what had happened at the previous medical but that she was ready to go again, that I was confident she had not received the appt. because she would have rung me to let me know as I was going to go with her next time, but she has had the MR today and they have not accepted her reasons as good cause for not attending and closed her claim.
We have made a rapid reclaim for ESA on grounds of worsening condition, she has appt. for next week to get GP letter in support of this, but wants to appeal the decision.
As she has not had the assessment we are not challenging the descriptors as usual - how would you approach this? I am confident that the letter did NOT go out - we have had numerous med certs, doctors letters that have been paid for, claim forms etc go missing in the large sorting office in Wolverhampton, but the DWP never accept this.
I would appreciate any direction you can give.
Thanks

Thank you, I'll send the SAR and also contact our MP - I have worked with his secretary before.
Thanks for your help again, very much appreciated.

Hi
Is there anything I can do to chase up a Subject Access Request? I sent one on the 3rd March but so far had no response. The DWP have sent the papers to appeal, I haven't received my copies yet, but it's just going to be a 'he said, she said' unless they are willing to provide proof that the letter went out.
Thanks again

Just as a quick update, DWP have said she will have to have a medical before she gets paid again. The ESA50 has been returned so we are waiting now for an appt. She was too distressed to claim JSA as she could not cope with the Jobcentre environment so we had no choice but to make a new ESA claim based on worsening condition, which her GP has supported with a letter. In the meantime she has not been paid since 17.2.16 and nothing on the horizon, so it has been food parcels. I am waiting for the Jobcentre to come back to me about the Hardship Allowance but not optimistic as she is not classed as having a disability and has no children.