Brave Girl, Quiet Girl

I have read a LOT of books over the years and this one had a most unique premise.

Brooke's car is hijacked with her 2 year old daughter in the back.
When the carjacker discovers Etta in the back, he dumps her on the side of a road and she's found by Molly, a 16 year old homeless teen.

What happens after this makes for a wonderful story.