The Sister Knot by Terri ApterThis was a present from my sister who heard the lady talk at the Hay Festival. It explores in some depth the love/hate relationships between sisters. I'm about three quarters of the way through it and it makes some fascinating points, though it is a bit repetative to read.
She uses Jane Austen's Emma as an example of a sister relationship. Emma's real sister has left home but Emma adopts Harriet as a surrogate sister whom she can boss around and who will look up to her. However she feels quite differently about her once she threatens to become her rival for Mr Knightley.
'Birds in their little nest agree' was the introduction to another chapter. Ms Aptor goes on to inform the reader that in most nests the stronger fledglings do their best to murder their siblings by depriving tham of food and warmth. She parallels this with the way sisters try to get the biggest share of both things and attention and often feel very aggressive about each other.
I haven't finished this yet but my sister is dying for me to get on to it so we can explore the psychology.