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.