Personal digital tax account with power of attorney

My client holds power of attorney for her mother, who has dementia. I have found answers on the forum to do with submitting the POA to HMRC, which my client will do. My question now is: is it possible for my client to set up a personal digital tax account for her mother? The mother has none of the forms of ID that are listed on the HMRC website. Following the death of my client's father, the mother has income above the various tax-free allowances for the first time in 2023-24 and so will in due course need to report - but it is not clear to me or to my client how to go about that, without digital access.

Hi MikeThexton,
For assistance regarding setting up an online account you will need to contact our online helpdesk.
Technical support with HMRC online services.
If your client is unable to set up an online account then once the POA details are submitted they can contact HMRC for assistance.
Income Tax: general enquiries
Thank you.