She is 85, lives in a rented council flat, has no assets. Apart from furniture in the flat ( which wouldn't be wanted or needed by anyone in the family), she maybe has a few hundred pounds in her bank account.
Despite this, I think it'll make things easier for DH if she has a will. ,My guess is that being an executor will make the winding up of things easier (eg closing her bank account, informing the council re her flat, etc).
It's going to cause her and DH some discomfort. Should we bother?