I'm driving myself potty, trying to find this series!
Originally seen being read by a Yr6 at work (I used to work in a school), thought it looked interesting, and binge read the whole series - it was quite enjoyable.
The main character (who is a girl) has always lived on a boat, as part of a tribe (maybe pirates?). I think her granny lives with her and is very mystical.
As the novels progress she meets other tribes eg who live on land, and in the sky/trees. In one of the stories she goes to a big meeting of the tribes.