PIP assessment cancelled

My daughter, who is 21, was diagnosed with Asperger's Syndrome in August this year. I helped her to make a claim for PIP. We live in Cardiff and she studies in Oxford so, when an appointment was sent, I asked if it could be changed to a more suitable date and that date was today. She can't travel alone on public transport if it involves changing trains as is the case with the journey from Oxford to Cardiff and there is no direct bus so my husband drove there on Saturday to bring her back. She was already very stressed when he took her to her 10.40 appointment this morning so my husband was furious to be told that the assessment was cancelled as the assessor was unwell. He asked if someone else could do it and was told the system was down and files could not be transferred. No-one phoned to tell her the assessment had been cancelled although they must have known before she left the house at 10am.
My husband is going to write a letter of complaint and will ask if she can be assessed on her form and 27 pieces of medical evidence we supplied rather than have to attend again, as this would cause her undue stress. I will also write to her psychiatrist for a letter of support.
Will it be to her disadvantage if she doesn't attend an assessment, given that she presented herself for an assessment this morning and this was not carried out due to Capita's ineptitude?

I phoned Capita this morning ad made a new appointment for the last day of the last week of the semester but when I told my husband, he said our daughter might want to stay in Oxford a week later to have fun with her friends. It was the latest appointment they had at the moment but I assured him I was allowed to change it once. Then I thought, this isn't the first appointment I've made; it's the first appointment after they cancelled. Will I be able to change it if it turns out not to be suitable? I won't even tell my daughter that she will have to attend again until I know what she will be doing after that last week as she can't cope with any more stress right now.

I think as they cancelled the first appointment you could still rearrange this one.

Obviously the more notice you have and can give the better but even if you ring on the day or the day before it is still the first cancellation you have instigated so if they say you can't make another you say we turned up for the first one and they cancelled it.

It is unlikely she will have classes that final week anyway so she could come home a day or two beforehand and go back if she wants to meet up with friends.