Ariadne Oliver never actually gets to be the detective. She's the sidekick, the foil, the mouthpiece for Agatha Christie's own mistakes and second thoughts. She may have intuitions and they may be correct, but she's never the hero, the real detective.
"'Journey's end in lovers meeting.'" Lenox laughed. "That is not going to be true for me." "Yes--yes, it is true. You are young, younger than you yourself know. Trust the train, Mademoiselle, for it is le bon Dieu who drives it." The whistle of the engine came again. "Trust the train, Mademoiselle," murmured Poirot again. "And trust Hercule Poirot. He knows.”
"I never guess. It is a shocking habit,—destructive to the logical…