Helly, does your friend collect carers allowence for this lady she lives with? If so, then the evidence is there.
Also has your friend been given power of attorney (spelt correct?) or, forget the wording, appointee by the secretary of state? If your friend has, then the evidence is there as they would have needed the lady's details such as full name, d.o.b, NI num etc.
If no, then get your friend to claim CA and to arrange to be made appointee. This can be done by asking CAB for advice or the local council housing department, they helped me with my hubby.
Good luck
Flower xx