The first white women who migrated west on the overland trails in the 1830s were

They were women accompanying their husbands in the westward movement.

For example, Marcus and Narcissa Whitman were among the early settlers of the West, pioneers of the Oregon Trail.  Their missionary party, headed to Oregon in 1836, included also Henry and Eliza Spalding.  The two wives, Narcissa and Eilza, were the first white women to cross the Rocky Mountains.