As a 7-year-old she married on 7 February 1402 Margrave Frederick IV "the Warlike" of Meissen (1370–1428), who in 1425 became the first Elector of Saxony, as Frederick I. The elector lost a large part of his army in the Hussite Wars in a battle in 1425 at Most. During Frederick's absence, Electress Catherine organized another army of 20,000 men, which rushed to Frederick's aid, but was defeated devastatingly in the Battle of Aussig in 1426.