A day later on Long Island, the cruel symmetry of tragedy was still too much for family, friends and officials to comprehend.
Evelyn Rodriguez, a fierce wisp of a mother who had gone to Washington and spoken privately with President Trump about MS-13, the transnational gang that killed her daughter Kayla Cuevas and a friend, Nisa Mickens, with a machete in September 2016, had dedicated her life to her daughter’s memory.
On Friday afternoon, two years almost to the date, she died fighting for her memory.
Ms. Rodriguez, 50, was run over by a car in Brentwood, Long Island, at the scene of a memorial for her daughter, the police said. Ms. Rodriguez and Kayla’s father, Freddy Cuevas, had been in a dispute with the driver about a shrine she had put up.
The police on Saturday had not filed charges and would only say an investigation was continuing. They definitively ruled out any connection between MS-13 and Ms. Rodriguez’s death.
“It’s beyond grief,” said Congressman Peter T. King, a Republican representing Brentwood who had become close with Ms. Rodriguez. “I can’t imagine a more horrific death for a child than being macheted to death and a more horrific death of an adult than being crushed by a vehicle.”
Barbara Medina, Ms. Rodriguez’s closest friend, was not there when Ms. Rodriguez was struck by the car, but said she had spoken with Mr. Cuevas, the longtime partner of Ms. Rodriguez, who gave an account of what happened.
“They had set up a shrine for Kayla’s second anniversary,” Ms. Medina said. “When they returned, the shrine was gone, the balloon had popped, as well as Kayla’s picture, everything was gone.”
Both Ms. Rodriguez and Mr. Cuevas were seen on footage recorded on Friday by News 12, a local television outlet, confronting the driver of a white S.U.V. — apparently about the disassembled shrine — about 90 minutes before the memorial was to begin. The police said the driver was related to a homeowner on the block.
As seen in the video, Mr. Cuevas waved his arms angrily and started walking to the back of the vehicle while Ms. Rodriguez stayed to the driver’s side. It was then, according to Ms. Medina, that the driver accelerated.
“She hit her, ran over her twice,” Ms. Medina said. “This was just senseless.”
The driver stayed to call 911, the police said.
The Suffolk County Police Department said on Friday that there had been a dispute over the placement of the memorial but would not comment further on the specifics of the events.
“She meant everything to me,” Mr. Cuevas said in a brief interview in which he was inconsolable except to praise Ms. Rodriguez’s strength and encouragement.
Arrangements were made for a wake on Thursday in Brentwood at the same funeral home that buried Kayla.
As tributes poured in from Mr. Trump on Twitter, Gov. Andrew M. Cuomo in a statement and from other leaders, it was clear that in her life, Ms. Rodriguez united people with her undeniable will. No mother, she said, should have to go through what she did.
Ms. Rodriguez grew up in the Bronx and in Puerto Rico; her public stance against illegal immigration, she said, was against criminals coming into the country and enrolling in schools.
“There was never a hint that she was blaming anyone political,” Mr. King said.
Ms. Rodriguez focused her message to Mr. Trump on getting more money for schools for gang-prevention programs and on safety measures there. She had sued the Brentwood school district for negligence in Kayla’s death and her dispute with an MS-13 gang member that the authorities said began at school.
Ms. Rodriguez had attended the State of the Union in January as a guest of the first lady, Melania Trump, along with the parents of Nisa.
In May, she worked with Mr. King to have Mr. Trump appear at a round-table discussion in Long Island. She helped arrange the attendance of the undocumented family members of four young Latino men who were also killed by MS-13.
“I never met anyone with more guts and more courage and never felt sorry for herself,” Mr. King said. “She never ever said, ‘Why is this happening to me?’ She always wanted to protect other people.”
Mr. King said he was on his way to the vigil when he found out she had died. When he got there, Mr. King said, streams of people were coming down the street unaware of what had happened. As word soon spread, people’s faces went blank, Mr. King said: “It was almost like, ‘What’s going to happen next to this community?’”
Last summer, as Ms. Rodriguez prepared to see President Trump for the first time at a speech before law enforcement officers on Long Island, she spoke of her activism.
Her words read like an epitaph.
“There are days where you feel like you want your world to end, just like your child’s,” Ms. Rodriguez said. “Then you realize you have a new purpose: to fight, so that your child’s death is not in vain.”