I read this fairly recently (couple of years) and when I went to lend it to my mum I couldn't find it in my bookcase and can't for the life of me remember what it is called. There are two childhood friends, one from a well off background and one from poor. One goes to jail for something (I think) and when is released works in a fairground. The other is living a nice comfortable life with husband and kids. They somehow bump into each other and I think the truth about what happened to cause one go to jail comes out. I think the chapters jump from the past to present day and they have different names in the past and present, so you don't know which girl is which. I think it builds up to the moment the 'big event' happens. You make assumptions which are then proven wrong at the end (hence why it was such a good book). I thought it was the ice cream girls, but it's definitely not that. I've read so many that they all get mixed up in my head! Help!
Oh - was just going to reply saying it sounded like the Ice Cream Girls If that isn't it, can't help - sorry. But you could have a search on Goodreads - if you put in Ice Cream Girls, it might come up with some similar books?
I agree with Clueless and Mimsy, it definitely sounds like The Wicked Girls to me. The premise is that two girls go to jail for the murder of a toddler and, on release, they must never meet again. I thought it was excellent on the ways the media shape our perceptions of both perpetrators and victims of crime.