In 1840 at age 16, while studying and living at Georgetown Seminary, she met Lieutenant John C. Frémont who was in Washington preparing a report on explorations (with Joseph Nicollet as commander) he had made between the Missouri River and the northern frontier of the United States. They became engaged, but her parents objected to a marriage at that time because of her age. Probably through the influence of Col. Benton, Frémont then received an order from the War Department to make an examination of the Des Moines River on the western frontier. Shortly after their return they were married on October 19, 1841.