Mary Lou McDonald is the leader of Sinn Féin - the party of Irish Republicans in the Irish Republic and in Northern Ireland. Ireland is going through a period of extraordinary change. Social attitudes have shifted profoundly on abortion, gay rights and the role of the Catholic Church. Now Brexit poses a challenge to the island, north and south. Can Sinn Féin take advantage?(Photo: Sinn Fein president Mary Lou McDonald after delivering a keynote speech for the first time during the annual party conference. Credit: Charles McQuillan/Getty Images)