Maddie believes she would know if Julie were dead.
This feeling is sparked the day Amélie comes home in hysterics because she and some of her school friends were near the Gestapo headquarters and witnessed the guillotine execution of a girl who had been a few years ahead of her in school.
Amélie reports that there were two girls by the guillotine, but she didn't stick around to see whether they executed the second one.
Maddie remembers the time she visited Paris with her grandparents before the Depression and went up in the Eiffel Tower with her granddad.
She knows the second girl must have been Julie, but she doesn't believe Julie is dead—she knows Julie must think she's dead, though, because of the pictures of the crash site, so she reasons that things aren't always what they seem.
Allied planes are going over every night, on their way to bomb munitions factories and launch sites.
Maddie knows the RAF is trying to avoid hitting Ormaie because of the civilian population, which is why Julie was sent to attack from the ground.
Maddie concludes that she won't believe Julie is dead until she actually sees it happen.