Dear Jane,
I am deeply sorry about your mother's situation. Her case is quite common for women her age, but is not something to overlook.
My recommendation for good sleep would be nuts in general (almond, walnuts, ...), cottage cheese, warm milk and fruits. They contain melatonin, a hormone that helps to regulate your sleep/wake cycle. Eating them can increase your blood levels of the hormone, helping you sleep more soundly.
Some food to avoid for a good sleep would be coffee, alcohol, dark chocolate and food high in protein. They rather contain caffeine, which prevents a well round sleep, or disrupt sleep when eaten too close to bedtime.
I wish your mother and you the best. Hope these help her to improve her sleep and well-being.
Best regards,
Expert