Other witnesses and the Gaza Health Ministry offered a slightly different version of events, saying that Ms. Najjar and other paramedics were walking toward the fence with their arms raised on their way to evacuate injured protesters when she was shot in the chest.

Ms. Najjar was a resident of Khuzaa, a farming village near the border with Israel, east of Khan Younis in the southern Gaza Strip. Her father, Ashraf al-Najjar, had a shop that sold motorcycle parts, which was destroyed in an Israeli airstrike during the 2014 war between Israel and the militant group, he said. He has since been unemployed.

The eldest of six children, Ms. Najjar did not score well enough in her high school exams to attend university, Mr. Najjar said. Instead, she trained for two years as a paramedic at the Nasser hospital in Khan Younis and became a volunteer of the Palestinian Medical Relief Society, a nongovernmental health organization.

Mr. Najjar, 44, said his daughter rose before dawn on Friday to eat and pray before the start of the daily, sunrise-to-sunset Ramadan fast. That was the last time he saw her.

When we met her at a protest camp in Khan Younis last month, she said her father was proud of what she did.

“We have one goal,” she said, “to save lives and evacuate people. And to send a message to the world: Without weapons, we can do anything.”

On Friday, she was less than 100 yards from the fence when she was bandaging the man struck by the tear gas canister, Ibrahim al-Najjar said. The man was taken away in an ambulance, and other paramedics tended to Ms. Najjar, who was suffering the effects of the tear gas.