It shows police helping her as she fled Islamic State (IS) after two young men slit the throat of Fr Jacques Hamel as he delivered Mass on Tuesday.
Saint-Etienne-du-Rouvray (76). Prise d'otages à ... by Letelegramme
In the footage, sounds of gunshots ring out as French police killed the two 19-year-old men, Adel Kermiche and Abdel-Malik Petitjean.
Fr Jacques Hamel was taken hostage alongside three nuns and two churchgoers.
The video was recorded by a 17-year-old boy who lives in an apartment facing the church in Saint-Etienne-du-Rouvray.
Armed police use shields to cover themselves as they bring the nun into a safe area.
The unnamed teenager told French newspaper Le Telegramme: "I woke up around 10am by the noise and the voices of the security forces.
"They were trying to evacuate the area because there is a school next door. At first, I thought it was a robbery."
He went on: "Someone shouted. Then I heard gunshots."
The attack in Normandy comes after 84 people were killed in a terror attack in Nice earlier in July and more than 100 were killed in an attack in Paris in November.
