Must we grant time off for employee to care for a grandparent?

Q. Our company has 30 full-time employees. One of our employees who is working on a key project has asked us for time off to take care of her grandfather, who has cancer, on days after he’s gone through chemotherapy. We know other family members are available to provide this care, and we are worried that it will be a hardship to have the employee away from work. Do we have to give the employee the time off?