Sillitti began her political career working in the office of Nassau County Legislator Dave Mejias. She then worked in the Department of Community Services for the Town of North Hempstead,[4] being appointed as deputy commissioner in 2010.[4] She later worked as director of legislator affairs and deputy chief of staff for Town Supervisor Jon Kaiman.[4]
From 2015 to 2020, Sillitti was the human resources director for the Nassau County Board of Elections.[4]
Sillitti was nominated at the Nassau County Democratic Committee Convention on February 11, 2020, after Assemblyman Anthony D'Urso announced he would be retiring.[4]
Sillitti ran on a platform to increase state funding for local schools and roads, reducing property taxes, and protecting Long Island Sound and drinking water.[4] She also advocated for stimulus relief from the COVID-19 pandemic and emphasized she would be accessible to her constituents.[3]
In late February 2021, after the Andrew Cuomo sexual harassment allegations became public, Sillitti was among a group of assemblywomen who issued a statement calling for an independent investigator to be appointed by Attorney General Letitia James.[6] She later pushed back against calls for his immediate resignation, being among 23 Democratic assemblywomen to say the attorney general's investigation should be completed first, in a split among New York Democrats.[7]