I've just been through all this in respect of my own Mother and know that the situation is not easy.

Unfortunately, unless your mother has already given Power of Attorney to your daughter, your daughter has no rights to do anything in your mother's name. It could be that the doctor is merely sticking to the letter if the law rather than being deliberately obstructive.

You need to follow the Public Guardianship Office link above and read about setting up a reciever (which could be your daughter) to handle your mother's affairs.

The customer information booklets and application forms can be downloaded, but unfortunately these things take time.

If your mother is in a Nursing home, how was she placed there? Either she is privately funded or had an assessment via a social worker. If a Social Worker is involved he/she may be able to help your daughter.