That Summer by Jennifer Weiner

 This is the story of 2 women named Diana, who suddenly find their lives intertwined. One is married to a wealthy lawyer, living in a big house in Philadelphia, with a teenage daughter. The other works in a restaurant on Cape Code. And what ties them together is what happened to one of them a summer a long time ago.

It's a good story about women standing up for themselves and making their own way through life. And about friendship and motherhood. Good read for the summer.