Maybe because Frida is five years older and Agnetha hasn't been out of the house for forty years.
Frida is now a German countess, she married a German count who then died.
Frida is half German half Norwegian, her father was a German soldier who was stationed in Norway during the occupation. Her family were treated as collaborators and had to flee Norway for Sweden after the war.
They both came from an age when women looked like women and not pre pubescent schoolgirls, so both of them would have sported a full bush.