Is it forbidden to bury a mother next to her mother in an adjacent grave, knowing that the mother's dying wish was not to be buried with her mother due to ill-treatment, and despite the possibility of burial in charity graves, but the shock of death affected the decision?

There is no objection to burying the mother in the aforementioned place. A will to be buried in a specific place is not obligatory to fulfill, as Al-Dumairi stated, quoting Al-Qaffal, that it is like someone who willed that so-and-so pray over them; it is not binding on the heirs, but rather recommended.