This woman is "Saiou-dai".
"Saiou" means "an unmarried female relative of the Japanese emperor".
"dai" means "substitute" or "replacement".
This lady disguise herself as "Saiou" today for this event,
she is not a real Imperial relative,
so she is "Saiou-dai" and not "Saiou".
In ancient times,Saiou was sent to Ise-jingu Shrine in order to serve God.
On the long way to Ise-jingu Shrine,she accompanied so many escorts and guards,security police,asssistants to protect herself from enemies,and take care of herself.
It took them about 6 days to go to Ise-jingu (Mie prefecture) from Kyoto by walk.
This event recreates those ancient people's procession,and is held in October of each year.
Now she is performing the ritual ablutions(ritual purification) in Oi-River.
Because of the big typhoon hit there on the previous day of the event,
it was so slushy underfoot,
so we could only see them from far away. We couldn't see them closely.
I'm happy if you enjoy the atmosphere of the good old days of Japan and ancient noble people.