I believe Sarah's response mirrors that of Abraham's in Genesis 17, when he heard this news for the first time. When Sarah laughs, the Lord asks Abraham why did Sarah laugh, saying "Can I really have a baby when I'm old?" This was essentially the same thought that had occurred to Abraham hearing it for the first time. I believe the Lord was asking Abraham why Sarah was reacting as though she was hearing this for the first time.
In Egypt, Abraham (Abram) failed to recognize the valuable role his wife would play in his own story. Even after many tests of faith, and the covenant being expanded to clearly include Sarah by name, in Gerar, only a short while after this encounter with the Lord, Abraham would again uncover his wife and expose her to the desires of another ruler, King Abimelech. Again, Abraham failed to love his wife, like the example set by Christ, to the point he was willing to lay down his life for her.
God did not rebuke Sarah because her lie, a shy denial of her own inner response, needed nothing more than a gentle correction. "No, you did laugh," was all the Lord had to say. What Sarah was truly in need of was the cover of a loving husband.
Notice, later when Isaac and Rebekah were childless that Isaac prayed for his wife. There is never any indication Abraham prayed for Sarah in her barrenness.
Also, clearly Sarah lacked faith. Faith is the evidence of things hoped for. At this point in her story, I believe Sarah had lost hope. There may have been little affection between her and Abraham, and as is often the case, her life experience to this point was playing a key factor in her view of God. God's purpose with Sarah would move her from a place of believing God was against her, to a place of knowing the love of God and the devoted affection of her husband. Check out Abimelech's rebuke of Abraham as he pays tribute to Abraham on behalf of Sarah. I believe God elevated this princess to her rightful place as the mother of the son of promise.