I agree, @groovylady . We were knocked back for my mum at first because a strange doctor was sent out and he asked her to go upstairs - which she did. (She had osteoarthritis and osteoporosis. Also had mild dementia at that point.)
He'd got her on a good day.
Social Work advised that I had to describe Mum on her worst day in the second attempt.
I recall that the form asked for her GP's details, and I'm sure that he would have given an account of her difficulties.
When I filled up the form for Dad, I had a better idea of what I was doing. I got a phone call from Edinburgh, asking whether Dad got up to the loo during the night.
"Yes, but there's no one helping him..."
"That doesn't matter. I just need to know whether he gets up during the night. That's fine. I'll tick the box saying he's entitled to the night-time allowance."
In my husband's case, his hospital ward contacted the Stroke Society and a chap came to the house. He filled up the form for DH. I did have to reapply a year later, however and I then didn't have to apply again.
ISTR that for all applications I enclosed an official printout/form for the medications being taken.
OP - might be worth while taking the form into a Citizen's Advice Bureau if you can. They know how to fill them in to get them passed first time.