Carolyn McCarthy, a former congresswoman from Long Island and fierce advocate for gun control, has died at age 81 after a years-long battle with cancer.

A former nurse, McCarthy got involved in politics following the December 1993 massacre on the Long Island Rail Road in which six people, including her husband Dennis, were fatally shot and 19 others, including her only child Kevin, were wounded by gunman Colin Ferguson.

Following Ferguson’s trial, McCarthy became an activist for gun control and later defeated incumbent Republican Rep. Dan Frisa in the 1996 midterms.

“I tell people, you don’t know the strength you have in you, until you are faced with what you have to deal with,” she told CBS News New York in 2014. “Anything I can do to make sure this doesn’t happen to anyone else, I will give my life to do that.”

A Democrat, McCarthy served the 4th Congressional District, which covers central and southern Nassau County, from 1997 until 2015 when she retired to receive treatment for lung cancer.

During her time in the House of Representatives, she worked to strengthen background checks, child-proof gun triggers, limit large ammunition magazines and disqualify those with mental health conditions and criminal records from buying guns.

“I just wanted to make a difference,” she told CBS News.

President Biden awarded her the Presidential Citizens Medal in January.

Nassau County Executive Bruce Blakeman said Thursday that he’d ordered flags to be flown at half-staff in McCarthy’s honor and that the county would find a street to name after her.

“I recently spoke with her about the 125th anniversary of Nassau County and invited her to attend the county’s gala as an honored guest,” Blakeman said in a statement. “Unfortunately, she wasn’t feeling up to it, but she expressed her best wishes and love for Nassau County. Carolyn was a true leader and a very decent person. She will be sorely missed.”