She had the right to throw the stone.

She looked at a sinner whose sin was beyond her comprehension.
She pitied the evident signs of distress, but her pity, although devoid of anger, was, in spite of herself, coldly wondering.
Moreover, Margaret had been guilty in the eyes of the girl of a much worse sin than the mere thievery of her book; she had murdered love.
Annie had loved Margaret greatly.

No, she loved her no longer, since the older woman had actually blasphemed against the goddess whom the girl had shrined.

Had Margaret stolen from another, it would have made no difference.

The mere act had destroyed herself as an image of love.