Hit the Road: by Caroline B. Cooney

This story features 16 year old Brittany Anne Bowman. When her parents leave for a vacation in Alaska, they leave Brit to stay with her 86 year old grandmother called Nannie. Brit ends up being the chauffeur for Nannie and all of her other 86 year old friends. Brit's new job is to take all of Nannie's friends to their college reunion. Although reluctant at first, she finallly realizes how important it is to them. Brit decides to do whatever it takes to get them to their reunion. The four people have interesting adventures on the way, including theft, kidnapping, and many lies.