Narcissa
Canonically, Narcissa has blond hair, unlike the rest of her family, and is the only one without an astronomy themed name.
Because of this, along with the fact that she is the third daughter of Cygnus and Druella, and they only required "an heir and a spare", I believe that Narcissa was the result of one of Cygnus' affairs. Narcissa is half veela, and Druella demanded that they raise her, as she was still a Black and still a pureblood. Her name was chosen by her mother, who was forbidden to contact her. Her mother agreed to stay away, thinking the Blacks could provide better for Narcissa, but demanding that on the day she gets her wand, a wand with her mother's hair as the core be presented before her. If it didn't choose her, then she could have another, but her mother was insistent that she at least try it, threatening to tell others and ruin the families reputation if they did not oblige.
In the books, Fleur Delacour has a wand with a veela hair core, so we know they can be used as such. As far as I know, we never learn Narcissa's wand core. I don't have the books, and I have only done minimal research, but I was unable to find one, so I believe that her wand does indeed have a veela hair core.
Narcissa was largely ignored by Druella in her childhood, which largely contributed to her personality as she grew older. Narcissa tends to be silent, and make herself underestimated, in order to have her opponent let their guard down, but she is a very powerful witch. She is also very cunning and clever, and she likely suspected that she was not related to her mother, but kept it a secret. She knew that it could drive a wedge between her and her sisters, not to mention the scandal it would cause, and she resented the mother who left her in the care of Cygnus and Druella. She had no desire to meet her.
This is loosely based off of the scene in Crimson Rivers where they talk about the rumour surrounding Narcissa's family and a possible affair on her mothers side.