I have suffered with the same fears and phobias as your daughter, at my worst i hadn’t left the house in years, hardly left my bed and they still stopped my money and said i had a sign on the dole!
However, i'm now on long term incapacity benefit , that was after a long battle with the powers that be, and have picked up a few tips along the way.
When you fill in the forms, you tell them what it is like on your daughters worst days.
Dont tell them she goes out once a year, just tell them she never goes out due to her panic attacks and agoraphobia, and then explain how this makes her feel, explain all the physical symptoms the panic attacks give her, ie the sickness, stomach pain, diareah ect
Also, write a letter to accompany the forms, my partner wrote 2 pages worth of information, going into great detail about how my mental illnesses are on on going every day battle, how often I have panic attacks (in my case, daily), how ill I feel even without the panic, every single symptom I have.
Is you daughters receiving any medication, or psychological help from a therapist or her doctor?
If so, ask her therapist to write a letter too.
When she has the medical examination, get her GP to request a home visit, as this will all help her case. And if she doesn’t see her doctor regular, ask her/him to come and see her to get them upto date with her condition.
*EDIT Just found out what ATOS is, my medical was with the old system, so i haven't yet had the "pleasure" of an ATOS review, i'm dreadingit now from what i've read but i hope what i posted helps in some way.