This older woman is a Russian Princess, and she is unusually ugly (M. Bouc calls her "ugly as sin," at one point, 1.3.27). Though she is feeble and elderly, as Poirot says, "I think, Madame, that your strength is in your will – not in your arm," (2.15.70-72). She has more strength in her convictions than she does physical strength.
Princess Dragomiroff was the godmother of Linda Arden's children and a close friend to the actress. She represents fierce loyalty and the triumph of mind over matter. The handkerchief found in Ratchett's compartment belongs to her.