Blood Sisters (1997)

Original title: Une vie pour une autre

Melanie can't stand her life anymore, a source of too much suffering. One day she decides to end it all and sets off in a stolen car on a suicidal race on the highway. But at a gas station, a somewhat eccentric old woman discreetly slips into the vehicle. Garance has a habit of randomly taking a seat in other people's cars, with only her suitcase and a binder bearing the title "The Flight Ceremony of the Northern Gannet". Melanie's suicidal plans are thwarted by this nuisance, whom she does not hesitate to inveigh against. But anger soon gives way to affection.