Sarah lives with her husband Joe Flanagan, and their two sons, in her native town, Kells. She is the second eldest daughter of James and Amelia Reilly.
She was educated in Our Lady of Mercy Primary School and Eureka Secondary School Kells. She then studied in NUI Galway, where she was awarded a BA in Legal Science, Sociology and Politics and an LLB Law Degree. Later she attended Griffith College where she studied for her professional solicitors exams. Her Masters of Rights and Social Policy was acquired in NUI Maynooth in 2013.
Sarah first ran for Fine Gael in 2009 for Kells Town Council. She topped the poll and was the first Fine Gael candidate to ever do so in Kells. During her five year tenure on the Town Council, Sarah was nominated and elected to the position of Town Cathaoirleach.
In 2014 Sarah ran on the Fine Gael ticket in the Kells District. Her campaign again proved very successful; she topped the poll for Fine Gael and took a seat on Meath County Council. In 2015 Sarah was nominated and elected to the position of Cathaoirleach of Kells District. Then in 2017, having proven her ability, Sarah was elected to the position of Chair of the Housing, Community and Cultural Strategic Policy Committee for the County. Other appointments of note include her service on the Louth Meath Education and Training Board and Blanchardstown Institute of Technology Board.