Kersna graduated from Lasnamäe General Secondary School in 1998 and from the University of Tartu in the field of journalism and public relations in 2005.
She worked as a presenter and editor at Eesti Rahvusringhääling from 1998 to 2002. From 2002 to 2004, she worked as head of public relations of the Federation of Estonian Student Unions. In 2004, she worked as the Chief Specialist at the Press Office of the Ministry of Rural Affairs, as Deputy Director of the Public Relations Department of the Ministry of Agriculture and Forestry of Estonia from 2005 to 2006, and was its head from 2006 to 2007. From 2007 to 2010 and again from 2012 to 2013, Kersna was the Media Advisor to the Government of Estonia; From 2010 to 2012, she was the Director of Government Communications of the Government of Estonia. From 2013 to 2015, she was the head of the office of Advisor to the Prime Minister of the Republic of Estonia.