How do you get a loved one to get a proper mental disorder diagnosis?

I would ask a medical professional their advice. But its great you're even asking, because too many people just wash their hands of people with mental health problems.

drive that person to a psychiatrist. don't tell them where they're going first.

you don't an accurate diagnosis is like an honest politician- yeah right

You go to a doctor or psychiatrist and get an opinion. then they will tell you what steps to take.

This is a very complex situation. Be careful

Unfortunately, sometimes people don't want to get help until they do something that requires the police to be called. In my state the cops would emergency petition her and force her to go to the hospital. The only thing you can do is talk to her and try to convince her to get help.

If your wife is divorcing you, she will not want your help. I would suggest talking to her family, if they don't hate you, or some of her good friends to try and encourage her to get help. You can't make anyone do anything against their will if they have some sense of sanity.

I suppose that the child is yours, correct? Contact child protective services. Advise them of what is going on. If this is a ploy to get her to stop the divorce proceedings, they will see right through you. If they feel an intervention is in the best interest of the child, and you're not looking out for yourself, they will act and place the child with you or the real father if they find her unfit. Are you ready to accept that?

I do find it troubling the way that you preface this by starting with "my wife is divorcing me and has mental illness". Then you further state that you "love" her. Since she is asking for nothing, is there a chance that she will do anything just to get away from you? And that you will do anything to make her come to her senses and stay, then justifying that by saying she is mentally ill?

You'd better have you act together either way and have proof of your claims.