People began filing through to pay their final respects on the first of three days of public viewing ahead of the funeral on Saturday.
The Vatican said it may keep the basilica open past midnight due to high turnout.
Socola said Francis encouraged young people to play a more active role in the church.
The nun said the moment when she stood in front of Francis’ coffin was “a moment to pray” for the entire Catholic Church and call for much-needed peace around the world.
“It was a great thrill to be there. And the most important thing is that it invites you to pray and be silent,” Socola said, before posing for a photo with other nuns and leaving St. Peter’s Square.
Francis died on Monday at age 88, capping a 12-year pontificate characterized by his concern for the poor and a message of inclusion, but also some criticism from some conservatives who felt alienated by his progressive push.