In 1531, she married Louis "Rodomonte" Gonzaga (1500–1532), an Imperial Captain of Charles V who was the son of Ludovico Gonzaga (her step-grandfather). Before his death, they were the parents of a son:
Vespasiano I Gonzaga (1531–1591), who became the Duke of Sabbioneta; he married Diana Folch de Cardona, a daughter of Antonio Folch de Cardona. After her death in 1559, he married Anna d'Aragona y Folch de Cardona, a daughter of Alfonso de Aragón y Portugal. After her death in 1567, he married Margherita Gonzaga, a daughter of Cesare I Gonzaga, Lord of Guastalla.
After Louis died, Isabella moved with his parents to Sabbioneta. Later, after quarrels with the latter, she moved to Rivarolo and then, in 1534, to her fiefs in southern Italy.
Second marriage
In 1534, she married Philip de Lannoy, 2nd Prince of Sulmona (1514–1553), the son of Charles de Lannoy, 1st Prince of Sulmona. Ludovico, the father of her first husband, opposed the marriage and obtained a decree from Emperor Charles V which entrusted Vespasiano's education to his aunt Giulia Gonzaga. Before the Prince of Sulmona died in 1553, they were the parents of five children: