Is a wife's wish for death for herself and her disabled child during childbirth considered a sin, or are these merely fleeting thoughts, given that she frequently praises and thanks God for His blessings?

The wife's statement "she and the child wish for death" is not a thought, but a wish that the Prophet, peace and blessings be upon him, forbade, saying: "Let none of you wish for death because of some harm that has befallen him. If he must wish for something, let him say: 'O Allah, keep me alive as long as life is good for me, and cause me to die when death is good for me.'" She should not wish for death, but rather thank God for His blessings and be patient with His decree. The child might be born healthy, and even if born with a disability, he might benefit you in this world and the hereafter, for how many disabled individuals have been dutiful to their parents. So, be patient and ask God for righteous offspring; this is better than wishing for death.