It's not always easy to determine whether someone is capable of making decisions. In some cases, it's obvious that a guardian and conservator is necessary -- for example, for a person who's unconscious or semiconscious, or who has advanced Alzheimer's or other forms of dementia. But many other people have physical or mental limitations that diminish but don't totally erase their decision-making capacity. In that case, a judge must weigh opinions and options.
If she can communicate, a judge may want to speak directly to her, or have a special court officer do so, in addition to reading reports from doctors and family members. The judge or court investigator will ask whether she understands the court proceedings, whether she wants a conservator, and whether she feels she can make her own decisions.
If, after a preliminary investigation, it's still not clear whether she needs a conservator, or who that conservator should be, the judge may appoint a separate lawyer to represent her in the court proceedings.
The judge might appoint a conservator but limit the conservator's authority to certain decisions only, with other decisions requiring a further court hearing.