(12) "Mental illness" means an illness that so lessens the capacity of a person to use self-control, judgment, and discretion in the conduct of the person's affairs and social relations as to make it necessary or advisable for the person to be under treatment, care, supervision, guidance, or control.
The term "mental illness" encompasses "mental disease", "mental disorder","lunacy", "unsoundness of mind", and "insanity".
Mental illness can contribute to ones ability to manage their own affairs. However, just having a diagnosis is normally not enough, in itself, for a court to adjudicate an individual Incompetent, and subsequently appoint them a guardian. More evidence would need to be presented regarding whether the individual is able to manage their own affairs as a competent person would do.
This is up to you. However, keep in mind that being adjudicated incompetent now does not mean that one cannot be restored to competency later in life. In fact, it's a great day in court when someone overcomes their earlier issues and prove that they are ready to make their own decisions.