Mrs. Hubbard, the character played on board the Orient Express by Linda Arden, famous actress and grandmother to Daisy Armstrong, is a comedy of the "American woman." Mrs. Hubbard is the only admittedly American woman on the train. Linda Arden heightens the character's Americanisms, Mrs. Hubbard is loud, need constant attention and espouses Western ideals. The first time Poirot encounters Mrs. Hubbard she is talking about the US, "you can't just apply American methods in this country. It's natural here for folks to be indolent. They haven't got the hustle in them...We've got to apply our Western ideals and teach the East to recognize them." Mrs. Hubbard uses less slang than Hardman, but still throws in an occasional "folks."

The character of Mrs. Hubbard is instrumental in the planning and carrying out of the murder. Mrs. Hubbard's cabin is right next to Ratchett and shares a communicating door with him. The night of the murder Mrs. Hubbard tells Poirot that Ratchett is a monster and that she is scared of him, she plants the idea that Ratchett is a bad person is Poirot's mind. The reader knows that Poirot already suspects Ratchett of evildoings, but Mrs. Hubbard does not. Mrs. Hubbard's call to the conductor in the early morning hours is also important to the case. By saying there was a man in her compartment, Mrs. Hubbard removed herself from suspicion since she was a victim of the attack. Mrs. Hubbard's hysterical behavior makes it easy to dismiss her as a suspect. Only an extremely talented actress could ever make up such fantastical speeches as Mrs. Hubbard. Mrs. Hubbard's downfall comes from one, simply mistake—the story about the lock on the communicating door. If Linda Arden hadn't said the bolt was below her bag, the case might have turned out differently. This piece of evidence, this obvious lie, called her into suspicion and confirmed her participation in the crime.