The video shows people running from Hamas gunmen as they try to escape a festival near the border that turned into a massacre.
At the end of the video, in the background, one of the women being chased squats on the ground, a gunman next to her. Moments later, the gunman raises his rifle and fires from close range at the woman, who falls over.
The video has no audio, but a cloud of dust rises from the ground as he pulls the trigger.
The woman was not identified by name.
Reuters verified the location of the footage, near Kibbutz Alumim, by the road layout, trees and a nearby building that matched the satellite imagery of the area.
Pressure is mounting on Israel to agree to a ceasefire in Gaza, where the Hamas-run government says at least 13,300 people have been killed, including at least 5,600 children.