Home Medical Assessment Refused - Advice Please!

My daughter (24) has suffered from severe ME and Fibromyalgia for 9 years. She is in the support group for ESA and we are dealing with her transfer from DLA to PIP. She is virtually housebound. Last week she received a letter for a medical assessment in a town which although geographically not far away, is really difficult to travel to. The car journey would take around 25/30 mins but we would have to allow 45/50 mins because traffic is so bad. Add to that waiting time, then the actual assessment and we would be looking at an outing of close to 3 hours - she would likely have a severe relapse and be far worse for months afterwards, I phoned ATOS and explained she had requested a home visit on the application form. On the basis, that the GP visits her at home, the person I spoke to cancelled the appointment and said someone would ring the GP. Today, we have received a second letter, saying she must attend an assessment at the same centre on another date. I see that you are only allowed to decline one appointment. Any thoughts on what we should do now. I'm really worried about this.

Thought I would give an update on this. Following your excellent advice, I spoke to the GP who confirmed he would write a letter. While I was waiting for this to be done I phoned ATOS to confirm where the letter needed to be sent. When I explained what I wanted, I was put on hold for a few minutes. When the lady returned, she said the 2nd appointment letter had been sent out in error and apologised profusely!!! She said my daughter had been put on the list for a home assessment and we would be hearing shortly.... that of course will be another battle I am sure but to me the initial refusal/then immediately back tracking without even waiting for the letter to arrives feels like a game of brinkmanship.