"An identical twin has to decide how much she is willing to sacrifice to save her sister from a violent death".
For me Give was always about love.
What would it be like to love an identical twin: so similar you even share dreams? A needy twin, you outgrow and have to get away from. You learn to love the man who helps you make that separation. But then he starts violently abusing you. You should leave him, but don’t because that would be admitting defeat, wouldn’t it? And perhaps there’s still a kind of love there. If that is Kate’s problem, maybe Sally’s is loving Kate too much.