Kit expresses sympathy for Mercy when she cannot join the girls in picking flowers. Kit asks Mercy, "how can you bear it, always staying behind?" How does Mercy respond?

From the text:

And Mercy had answered serenely, "Oh, I settled that a long time ago. I remember it very well. Father had carried me to the doorstep, and I sat there watching the children playing a game in the road. I thought of all the things I would never be able to do. And then I thought about the things that I could do. Since then I've just never thought much about it."