Elderly patients can definitely suffer from depression, even in its severe form. It is very common for the elderly to feel mildly depressed after the loss of their partner, as this can be a very life-changing event. Normal grieving process involves feeling sad for some time after the loss of a loved one. However, it is important for you and the rest of your family to watch out for signs of "pathologic grief," which can be a signal that her grief is converting into depression. Things to watch out for are:
1) Symptoms after 6 months
2) Significant weight loss
3) Thoughts of hurting herself, making a plan to do so, or an attempt to do so
4) A feeling that life is empty
If you notice some of these symptoms, your grandmother should go to see her primary care physician
and get a referral to a psychologist
for further care. Pathologic grief should be treated like depression, and she may benefit from medications, counseling/therapy, or both. In the meantime, you and your family can also help by keeping her on a regular schedule of sleep, diet, hygiene, and social activities with her friends and family.