Matilda question

OK, so I usually pride myself on remembering book titles and authors, but there is one that has utterly escape me! I remember the plot very well...It is told from the point of view of a mother whose teenage daughter accidentally hits another young girl with her car and kills her because she is distracted by a stray dog she and her best friend found. The book flashes back and forth between present time and the mothers relationship with her daughter, to past and the mother's relationship with her own mom. The book ends with the daughter going away to work in New Mexico because she has issues dealing with her key role in the death of the girl she hit with her car...deals a lot with family relationships (i.e the women and her sister who has 3 kids by three different men)
This book wasn't that great, although the plot was so that it stuck in my mind and it has been driving m CRAZY not to remember the title/author. If anyone has even the slightest idea I would love to hear it!
Thanks one and all :)