I definitely agree with fluffy. Some word is important, whatever that word may be. And it's also important to offer support to the main caregiver from the family. It's not easy caring for a terminally ill person. Just knowing someone is thinking about the person doing it can also be surprisingly helpful. Flowers, some jam, or a recent photo might also be appreciated by the patient.
Some years ago, my grandmother's best friend was very ill and went into essentially the hospice wing of the retirement community she lived in. After her death, there were very few possessions to be cleared out because she'd more or less divested herself of most of her worldly goods by the time she got too ill to care for herself. In the end, the things she kept were a photograph of my family, a couple cards I and other members of my family had sent her over the past few months, and a letter my brother wrote her when he graduated college. Apparently she would have the nurses read that letter to her almost every day, and she told everyone proudly about us. She was a wonderful woman. It feels good to know that those cards and letters meant so much to her.
So write. Write something. Anything. Just let her know she's remembered and cared about.