How do you know she was suffering with enough certitude to let her die?
International Federation of Catholic Medical Associations, International Congress: Life-Sustaining Treatments and Vegetative State: Scientific Advances and Ethical Dilemmas
www.vatican.va
I should like particularly to underline how the administration of water and food, even when provided by artificial means, always represents a natural means of preserving life, not a medical act. Its use, furthermore, should be considered, in principle, ordinary and proportionate, and as such morally obligatory, insofar as and until it is seen to have attained its proper finality, which in the present case consists in providing nourishment to the patient and alleviation of his suffering.
In Catholic teaching, taking a loved one off a heart-lung machine is permissible as an extraordinary treatment. Providing nutrition through a feeding tube is ordinary treatment.
Consider what a mother naturally does for her child who as an infant cannot feed itself or control its environment. She feeds her infant and controls its environment. However, mothers do not breathe or provide the means to circulate the infant's blood.