In Assassin's Creed Syndicate, the main female playable Frye twin is Evie Frye.
Evie and her twin brother Jacob are Assassins who travel to London in 1868, during the Industrial Revolution. They oppose the Templars and their allies while trying to free the city from criminal and political control.
Evie is presented as the more methodical and stealth-focused of the two siblings. Her missions emphasize infiltration, investigation, and the search for a Piece of Eden connected to the First Civilization. Jacob's missions more often emphasize direct combat and gang warfare.
Jacob is also playable throughout the game, so Evie is not the only protagonist. The game alternates between the twins and includes missions designed around each character's strengths. Lydia Frye, their descendant, appears in a later sequence set during the First World War.