Is any thing too hard for the Lord? Heb. Hid from God? So the sense is: Though she laughed only in her heart, it is not unknown to me. Or rather, too wonderful for God to effect? Which best suits with the following words.
Related Commentaries of Genesis 18:14
Genesis 18:14
14 Is any thing too hard for the LORD? At the time appointed I will return unto thee, according to the time of life, and Sarah shall have a son.