Charles Ellicott Commentary Jeremiah 41:10

"Then Ishmael carried away captive all the residue of the people that were in Mizpah, even the king`s daughters, and all the people that remained in Mizpah, whom Nebuzaradan the captain of the guard had committed to Gedaliah the son of Ahikam; Ishmael the son of Nethaniah carried them away captive, and departed to go over to the children of Ammon." — Jeremiah 41:10 (ASV)

Even the king’s daughters. —We find in Jeremiah 39:6 that the sons of Zedekiah were slain at Riblah. The daughters (the word was probably used generally for all the princesses of the royal house) were spared, and consigned to the protection of Gedaliah.

In taking possession of them, Ishmael was asserting, according to Eastern custom, his claim as the representative of the royal house. The Ammonites had been in alliance with Zedekiah (Jeremiah 27:3), and Ishmael counted on finding a safe refuge with them. It would seem, indeed, from Jeremiah 40:14, that he had been sent, or was believed to have been sent, by the king of the Ammonites for the very purpose of the murder of Gedaliah.