Extending time limit for notification of change of circs

My client’s circumstances changed, but for various reasons putting stress on her health and life, she did not inform of the change to increase her DLA. She also did not know there was anything to inform about, and did not have the physical and mental health to obtain advice.
When an advice worker advised her, she immediately requested a supersession of her DLA.
In the form she requested the time limit to notify the change be extended (she was still within the 13 months) for the reasons given above. So that the supersession could be from the earlier date.
This was made under Reg 8 SSCS (D&A) 1999.
She was sucessful in getting her award increased from the date of the advisor’s call.
Physically she easily meets the increased need.
The only issue was the backdating-which is the subject of the appeal-and whether it satisfies the DM re: Reg 8.
The DWP response states she was fully aware and mentally competant to advise the Dept and those are the reasons for refusal.

For the appeal, I suppose whats needed is evidence of the circumstances.
I’m a bit worried she stated she didnt know there was anything to inform about - ie ignorance of the system.
I guess she would have been able to find out had she and her family been well enough.

I cant find any case law. Anyone help?
Also the link to the DM Guidance-I’ve searched but its not opening.

Thanks.