Evelyn Rodriguez, who became a vocal advocate for victims of gang violence after members of the transnational gang MS-13 were charged with killing her 16-year-old daughter, died after being struck by an S.U.V. on Friday — just before a memorial service for the second anniversary of her daughter’s death.
The Suffolk County Police Department said that she had been involved in a dispute with a driver around 4 p.m. near where the ceremony was to take place, and that the vehicle struck her as the driver tried to leave.
The memorial was set to be held in Brentwood, on Long Island, in a suburban cul-de-sac not far from where the bodies of Ms. Rodriguez’s daughter Kayla Cuevas and her friend Nisa Mickens, 15, were found.
Ms. Rodriguez, 50, a vocal advocate for crime prevention who was invited to President Trump’s State of the Union address in January, had been preparing for the memorial on Friday evening to commemorate the anniversary of the day her daughter’s body was found.
On Friday night, Mr. Trump tweeted about her death. “My thoughts and prayers are with Evelyn Rodriguez this evening, along with her family and friends,” he wrote.
On the day before the memorial, Ms. Rodriguez told Newsday that people attending were going to bring candles and balloons to remember Kayla and Nisa. “It’s a fight that I have to continue to make sure all communities are safe,” she said.
In a statement on Friday night, the Suffolk police said that Ms. Rodriguez got into an argument with the driver of a sport utility vehicle regarding the placement of the memorial.
The police did not name the driver but said she was a relative of someone who lives nearby. After she tried to leave and the S.U.V. struck Ms. Rodriguez, the statement said, the driver remained on the scene and called 911.
Ms. Rodriguez was taken to Southside Hospital in Bay Shore, N.Y., where she was pronounced dead. Homicide detectives were investigating the episode.
Footage recorded on Friday by News 12, a local television outlet, appeared to show a verbal confrontation between a person driving a white S.U.V. and Ms. Rodriguez, who was standing near the front of the car with her husband. News 12 reported that shortly after that confrontation, the vehicle accelerated toward Ms. Rodriguez and ran her over.
Timothy Sini, the Suffolk County district attorney and a former police commissioner who investigated Kayla’s and Nisa’s murders, said he could not comment on the details of the investigation.
“But I will state, because it’s important to make this clear, this had nothing to do with MS-13, this was not an act by MS-13, or done in coordination with the gang in any way,” he said.
Mr. Sini added that he was “heartbroken” by her death. “Evelyn was a true partner in our fight against MS-13.” he said. “As a parent, I cannot imagine how one is able to function after losing a child, particularly to murder. And she took that grief as a force to effect positive change. She accomplished a lot; she was a tireless advocate for her community.”
Gov. Andrew M. Cuomo said in a statement late Friday that Ms. Rodriguez “showed tremendous courage by dedicating herself to the disruption of gang violence throughout her community.”
“As she stood by my side as we fought back against MS-13, I stand with her family tonight,” he said.
MS-13, which is also known as La Mara Salvatrucha, has roots in Los Angeles and El Salvador and has existed for more than two decades on Long Island. Officials have said that thousands of school-age migrants came as unaccompanied minors to the Brentwood School District over the past several years.
When members of the gang were charged in the murders of Kayla and Nisa, the case became a flash point for the Trump administration’s crackdown on illegal immigrants.
Both President Trump and Attorney General Jeff Sessions have visited Long Island and met with Ms. Rodriguez to discuss gang violence there. And in January, Ms. Rodriguez was invited to the White House to attend the State of the Union address.
“I’m not here for anybody’s political gain,” Ms. Rodriguez told The New York Times shortly before that event. “I just want what’s right to be done. Everybody should put their political agenda aside and think about what’s going on in our country.”
Barbara Medina, a close friend of Ms. Rodriguez who worked with her to advocate on behalf of MS-13 victims, was in shock on Friday night. “She was relentless,” Ms. Medina said. “She was a ball of fury and with positive energy. She was a warrior. She was determined for justice for her daughter.”
Andrew R. Chow contributed reporting. Jack Begg contributed research.
Follow Jacey Fortin on Twitter: @JaceyFortin.