I can vouch for the truth of this. It may not be the exact same circumstances but in my own life I've experienced God's freeing Power from mental illness despite being told by medical professionals that the answer was in medication. The world can only attempt to treat and cure and stabilise us and the troubles inside ourselves with the worlds mean - medication, breathing techniques, minfulness, etc. But we serve a God who is not conformed to this world. Of course God created doctors and medicine for us to use for our physical ailments. But when I read the Gospels I see that every case of insanity or what we would call mental illness etc, was demon possession or demon oppression, and Jesus and the disciples dealt with it by addressing the root cause - demon powers. I therefore truly believe that the majority of mental illness in the world today is a result of either demonic possession or demonic oppression (as children of God we cannot be possessed, but we can be demonically oppressed from the outside). I have found freedom from deep depression through filling my mind with the word of God, proclaiming His word, and verbally binding the enemy in Jesus' name.
Not only that, but 10 years ago I experienced a trauma in my life, and from that day forward I was plagued by a spirit of fear which manifest in certain situations. I was told by the professionals that this is normal when you experience trauma, and that while I could try to manage it with breathing techniques and the likes, I would just have to learn to live with it. But do you know what? Four long years later I surrendered my life to Jesus and soon after He delivered me from that spirit of fear in one MOMENT! This was an immediate deliverance for me, and of course not everything will happen immediately. We must learn to use the authority God has given us through Jesus Christ to combat the spirit of fear and anxiety which are NOT from God but from Satan, and to use His very word to renew our minds and conform them to God's truth, and refuse to allow the devil to make us feel like there is no way out of our present circumstances. We must fight the fight of faith in all areas of our lives, depression and anxiety included. I want to encourage anyone here experiencing what the world calls mental illness that you do indeed have a sound mind in Christ and it's devil who wants you to believe otherwise and we must combat that liar with the Word of God and apply His word to our lives and we will see freedom, praise the Lord.