Why was Catherine de’ Medici appointed regent during the siege of Metz in 1552?

Catherine de’ Medici was appointed regent in 1552 specifically to manage affairs during the absence of her husband, King Henry II of France, while he was away at the siege of Metz.1

While she held this position during the King's absence, she generally lived a private life during this period, focusing on the supervision of her children's education. This appointment was a temporary administrative measure necessitated by the King's military campaign against the Habsburg emperor Charles V, during which France captured the bishoprics of Toul, Metz, and Verdun.12