“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.