“I am confident that the deceased was unaware of what was happening.” She lacked the capacity to act on her own, and although she grunted or even said “yes”
When called “mum,” this was just a reaction to being addressed directly and did not signify that she agreed to sign the will or acknowledge its contents.
“During the reading of the will, she seemed totally blank and, with the exception of one instance, she solely answered her daughter.