In 2012, Fernandez volunteered for Mark Gjonaj's campaign for New York State Assembly. After Gjonaj won, Fernandez joined his staff as executive coordinator. She later rose to be Gjonaj's Chief of Staff.[3]
In 2017, Fernandez joined the staff of New York Governor Andrew Cuomo as the representative of his office to the Bronx.[2]
Following the election of Mark Gjonaj to the New York City Council, the 80th New York State Assembly district was left vacant and a special election was held on April 24, 2018. Fernandez ran on the Democratic and Independence party lines against Gene DeFrancis, who ran on the Republican, Conservative, and Reform party lines.[4]
In late 2018, Fernandez ran for a full term in the Assembly. She was unopposed for the democratic nomination. Fernandez ran on the Democratic party line against Louis Perri, who ran on the Republican and Conservative lines. Fernandez won over 81% of the vote.
In August 2022, Fernandez won the primary for New York's 34th State Senate district.[5] She went on to win the district in the general election and began serving in January 2023. She is the sponsor of Senate Bill S6142 (the OMNY Privacy Act)[6], which, if passed, would prohibit "the disclosure of individualized fare payment data by the metropolitan commuter transportation authority and the New York city transit authority."[7]