At the 2005 European Athletics Junior Championships in Kaunas (Lithuania) Horna finished in 8th place of the 800m race. She was eliminated in the semi-final of the 2006 World Junior Championships in Athletics in Beijing, and in the first heat of the 2009 European Athletics Junior Championships in Kaunas, both times over the 800m distance. In 2009 she won her first individual national title during the German Indoor Athletics Championships. She won the silver medal at the 2009 and 2010 German Athletics Championships. In 2013 Horna won the title over the 1500m distance at the German Indoor Athletics Championships, and she defended her title in 2014.