The OP proposes an idea that is wonderful on paper (and sometimes might actually work). However, this is often a worthy concern but impossible.
Mental illness usually develops between the ages of 10-11 through 25-26. There certainly are exceptions to this range. The hormonal changes that precede puberty are influential in this, and so are genetics. But it is wholly possible that the condition is not detected until the 20’s. I am aware of cases where a couple married, with both of them symptom free, and one of them later developed a serious mental illness. There is no one to blame or hold responsible. Similarly, the development of the mental illness is seldom an overnite experience, but rather the array of symptoms develop gradually. This makes the issue complex in that the evaluating professional is trying to assess a moving target.
I would urge anyone seeking evaluation (if the need presents) seeking a professional that is trained to work with that age group. All mental health evaluation involves a certain amount of guess work, as it is a soft science. But the more experienced and educated guess is a better bet. An underscore is that tefiloh is warranted, as the ultimate healer is HKB”H. We have our hishtadlus to make, and our obligation is to do this with the best of responsibility. Then, Hashem takes over and guides these professionals and their interventions with Syatta Dishmaya.