Ladder of Years by Anne Tyler

Delia Grinstead has spent most of her adult life quietly working in the office of her father and then her husband, both doctors in their small Maryland community.  She senses that her young adult children would rather be anywhere than in a room with her and feels invisible to her husband.  In the midst of a tiresome beach vacation with her sisters and her family, she takes advantage of a ride out of town and never looks back.  She creates a whole new life for herself in another small town and even when she reconnects with her family, chooses to stay in her new life.  As family members dance around their real feelings for one another, Delia finally needs to make a choice.