My sympathy, and a prayer, regarding your grandmother and your loss.
You aunt had to do what she thought was right.
Excerpts from the Catechism of the Catholic Church
2277 …Thus an act or omission which, of itself or by intention, causes death in order to eliminate suffering constitutes a murder gravely contrary to the dignity of the human person and to the respect due to the living God, his Creator…
NB 2278 **Discontinuing medical procedures that are burdensome, dangerous, extraordinary, or disproportionate to the expected outcome can be legitimate; it is the refusal of “over-zealous” treatment.
Here one does not will to cause death; one’s inability to impede it is merely accepted.
The decisions should be made by the patient if he is competent and able or, if not, by those legally entitled to act for the patient, whose reasonable will and legitimate interests must always be respected.
2279 Even if death is thought imminent, the ordinary care owed to a sick person cannot be legitimately interrupted. The use of painkillers to alleviate the sufferings of the dying, even at the risk of shortening their days, can be morally in conformity with human dignity if death is not willed as either an end or a means, but only foreseen and tolerated as inevitable. Palliative care is a special form of disinterested charity. As such it should be encouraged.
2299 The dying should be given attention and care to help them live their last moments in dignity and peace. They will be helped by the prayer of their relatives, who must see to it that the sick receive at the proper time the sacraments that prepare them to meet the living God.