All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
First of all, we ask Allaah The Almighty to give your wife rapid recovery from her illness and we ask Him to relieve you and her from grief and distress.
Dear brother, we advise you to supplicate Allaah for her as much as possible as He responds to the supplication of a person who is desperate and He removes evil; Allaah Says (what means): {Is He [not best] who responds to the desperate one when he calls upon Him and removes evil and makes you inheritors of the earth? Is there a deity with Allaah? Little do you remember.} [Quran 27:62]
Secondly, we recommend you to perform Ruqyah for her with the Quran, legislated mention of Allaah and Prophetic supplications because Ruqyah is beneficial, Allaah willing.
Thirdly, there might be a need to consult trustworthy and experienced psychiatrists, as they may prescribe a medication for her that would alleviate her depression, so that she may think and act in a proper and sound manner.
Fourthly, there is no doubt that what your wife feels is nothing but one of the plots of the devil to make her sorrowful and to ruin her life. Indeed, the devil is an enemy to the human being as Allaah Says (what means): {Indeed, Satan is an enemy to you; so take him as an enemy. He only invites his party to be among the companions of the Blaze.} [Quran 35:6] The best solution, in this case, is to completely repel the devil’s whispers, to have a good opinion of Allaah, to have hope in Him and to remember His vast Mercy and think good of Him; Allaah Says (what means): {Say, “O My servants who have transgressed against themselves [by sinning] do not despair of the mercy of Allaah. Indeed, Allaah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful.”} [Quran 39:53] Allaah also Says (what means): {Those who avoid the major sins and immoralities only [committing] slight ones. Indeed, your Lord is vast in forgiveness.} [Quran 53:32] Besides, a Qudsi Hadeeth reads: “I am according to what My Slave thinks of Me, if he thinks good of Me, then he will be treated accordingly, and if he thinks bad of Me, then he will be treated accordingly.” [Ahmad - Al-Albaani and Arna’oot classified it as Saheeh [sound].
Allaah Knows best.