DLA to PIP migration at 16 for autistic teenager

So my daughter who was on DLA is refusing to engage with the PIP telephone assessment due to her crippling anxiety and autism. She doesn't speak to anyone she doesn't know on the phone and often won'teven speak to family. A face to face is absolutely out of the question. When I spoke to the assessor she suggested that I call DWP customer services and ask them to appoint me as her Appointee so I can speak on her behalf. However I understand that to be appointed there would need to be a visit/interview with my daughter from DWP to check this is appropriate. Obviously she would not engage with this as it would again involve speaking with a stranger and this would be very distressing for her. If anyone comes to the house she locks herself into her room and gets very upset. I feel as though we are in a catch 22 situation. Any suggestions please? Many thanks