Who is The Princess Dragomiroff from Murder on the Orient Express and what is their importance?

The Princess Dragomiroff is, of all the passenger/suspects, perhaps the most similar in terms of the personality she presents and the truth of who she is. The Princess is an elderly Russian aristocrat, who is described as both willful and autocratic. When she is confronted with the truth by Poirot, she admits to having been a devoted friend of Linda Arden, as well as godmother to Mrs. Armstrong. She doesn't admit, however, to being a member of the conspiracy to kill Ratchett, which is the only point of disparity between what she presents and who she is. The Princess is the first among the passengers to suggest that Ratchett's murder might be considered a good thing..... she also suggests that Poirot's presence on the train was fated.