Elizabeth married at the age of 19, and she and her husband lived in Manhattan where they attended Trinity Episcopal Church. The Setons had five children and also raised her husband's six younger siblings. Elizabeth was widowed in 1803, and shortly thereafter she became a Roman Catholic.
She began an academy for young women, but met a priest who was a member of the Sulpician Fathers. Elizabeth was invited to move to the community in Emmitsburg, Maryland, where she founded St. Joseph's Academy and Free School, so that Catholic girls could be education. She also established a community, called the Sisters of Charity, which founded a religious school or poor children---essentially the beginning of parochial schools in this county.
My daughter went to Seton Hill University in Greensburg, PA (below), still maintained by the Sisters of Charity (and not to be confused with Seton Hall University in New Jersery). Other schools and several churches are also named for Mother Seton.
The Roman Catholic site has a good piece on her: http://www.americancatholic.org/Features/Saints/saint.aspx?id=1250&calendar=1