Whether AI can help with mental disorders is a question of whether it can figure out consciousness or not, or at least how much of it it can presently understand. Much of the human mind is a great mystery; just as how our understanding of human biology and anatomy leads to advancements in surgery, vaccines, rehabilitation etc., a growing science in human mind is how we can understand the nature of psychological illness and eventually remedy them.

If mental illnesses for example were discovered by AI to be a result of physical malfunctions in the brain or its sub-organs or find such ailments to be a product of chemical imbalance, or even a result of our mismatched intelligence and biological tendencies (also rooted in parts of the brain), then perhaps it can employ physically reconstructive solutions to help its victims.

But if mental illness remains elusive and appear deeply rooted, intertwined or emergent with consciousness itself, and it struggles with understanding the nature of it, then it will have a very difficult time solving "conscious illnesses", understanding the nature of anything is the key to manipulating it

The wild thing here is, when we make AGI or ASI, it itself might have mental illnesses, it is after all, a thinking, possibly conscious being; there is the possibility that it ends up suffering the same things we suffer from.

The bottom-line is, Actual AI and the Human mind/intelligence are both subjects we are not very developed in, to the point where predicting how they will interact can feel like speculation.

That said, the nature of both fields are deeply similar (that of consciousness and intelligence), and so advancements in one of them will inevitably lead to insight and progress into the other.