LONDON — When about 100 heavily armed police officers and soldiers took position shortly after 4 a.m. Wednesday outside the building in the Paris suburb of St.-Denis where the presumed ringleader of the Paris attacks was holed up, a young woman appeared in a window.

“Help!” she shouted, according to the reports of witnesses. “Help me!”

But Hasna Aitboulahcen, a cousin of Abdelhamid Abaaoud, the Islamic State jihadist believed to have orchestrated France’s deadliest terrorist attacks to date, did not fool the officers, who suspected a trap. Two hours and 5,000 rounds of ammunition later, this 26-year-old daughter of a Moroccan immigrant was dead, in the end not by becoming the first woman to blow herself up in a suicide vest on Western soil, as first suggested by the authorities — but by being killed in a fierce battle with the police.

Ms. Aitboulahcen has been widely portrayed in the news media as a onetime wild child, at least by fundamentalist Muslim standards: smoking, drinking, staying out late, wearing cowboy hats, having lots of boyfriends and rarely going to the mosque. A widely circulated photograph shows her lying in a bubble bath, smiling coquettishly at the camera. In short, she seemed to be the thoroughly secular antithesis of how the pious Islamic State expects its women to behave.