Why does Katherine work on the geriatric ward in Forever?

Katherine volunteers in the geriatric ward because she didn;t get to know her own grandparents before their deaths. She was afraid of her grandparents (paternal) and didn't enjoy the time she spent with them. When her mother’s father got sick, she already had an established, loving relationship with him, and as a result, she came to understand that she'd missed out on the same type of relationship with her father’s parents. Katherine then realized that there was nothing to fear, and that she wanted to make older people feel better before they died.