So B. It, by Sarah Weeks

There are only a few things that Heidi knows for certain:  she has incredible luck (winning every time she plays the slots, for example), her family's friend Bernie is afraid to go outside the house but is otherwise her primary caregiver, and her mother's name is So B. It. 

At least, that's about all she thinks she knows about her mother.  Mom is a bit slow and isn't much for communicating (she knows only twenty-three words) and can't tell her much.  Still, Heidi is determined to find her roots.  When she finds an undeveloped roll of film in her Mom's things, it sets off a chain of events that sends Heidi on a cross-country trip.

A surprising and delightful book.  I'm not a big fan of children-abandoned-to-danger stories, but the scary stuff in this one is kept to a minimum (maybe because of Heidi's innate luck?).  And the book has many things going for it.  The characters are memorable and quirky.  The story is well-paced and engaging.  And while the ending is drawn out, it is satisfactory, without trying to tie up every loose end.