Audrey Niffenegger said this quote

The hardest lesson is Clare’s solitude. Sometimes I come home and Clare seems kind of irritated; I’ve interrupted some train of thought, broken into the dreary silence of her day. Sometimes I see an expression on Clare’s face that is like a closed door. She has gone inside the room of her mind and is sitting there knitting or something. I’ve discovered that Clare likes to be alone. But when I return from time traveling she is always relieved to see me.