Basically, guardianship over the person means that they can have her committed against her will.
This unfortunate woman is undoubtedly unstable, possibly suicidal, and needs loving protection from herself. It's a good thing she wasn't beaten, raped or murdered while out on the streets that night.
With all their money, one would think Joan would get proper care and attention from her children and even her ex-husband, Teddy. Maybe she's such an embarrassment to the lofty Kennedy name, that they subconsciously want her locked up somewhere (or worse) forever.
Reminiscent in some ways of the oldest Joe Kennedy retarded daughter who was tucked away outside the realm of public notice until she passed on.
On the other side of the coin, hardened alcoholics can be uncontrollable even with all the help in the world. It may be that nothing can help Joan any more, short of chaining her to her bed post with a 24-hour guard.
What a mess. Much money, much unhappiness in that family and its extended circle of relatives and ex-relatives.
Leni