Lucius Malfoy was a well known Death Eater and eventually Draco Malfoy became one as well. But what about Narcissa Malfoy, Lucius' wife and Draco's mother? She certainly spent a great deal of time around Voldemort and her husband, but I don't recall her ever being explicitly described as a Death Eater.
So was Narcissa Malfoy a Death Eater? Or was she a non-Death Eater permitted to be in the company of Voldemort?
J.K. Rowling explicitly stated in a web interview with fans that Narcissa Malfoy was not a Death Eater:
No, she never had the Dark Mark and was never a fully paid-up member. However, her views were identical to those of her husband until Voldemort planned the death of her son.
As for why she was able to be so close to Voldemort despite this, I imagine that it was mostly because of her relation to Lucius and Draco, as well as the fact that her and her husband's house became Voldemort's base of operations, so he just got used to having her around.
Narcissa never actually joined the Death Eaters herself. None of the Death Eaters refer to her as one, not even the ones who are directly related to her. She doesn’t show up to the meeting at the graveyard, and Dark Lord doesn’t mention her as one of the Death Eaters he’s expecting. Lucius does attend, however, and isn’t questioned on his wife’s faithfulness. The Dark Lord seemed to be doing a sort of “roll call” and assessing the loyalty of all his Death Eaters - yet he doesn’t seek Narcissa.
However, she was the wife of an important Death Eater and the sister of another important Death Eater, so she would have been permitted to be in the company of the Dark Lord and the Death Eaters because of them. Later, her son Draco also became a Death Eater, giving her yet another connection to their cause.
The Malfoy family proved to be quite useful to the Dark Lord, due to their wealth and influence in the wizarding world. They seemed to be the single richest and most influential family among the members of the Death Eaters. They could provide the Death Eaters with a lot of money, and used his influence in places like the Hogwarts board of directors and the Ministry of Magic to their benefit. Lucius and Narcissa even allowed the Dark Lord to use their manor as the headquarters for the Death Eaters during the second wizarding war.
Narcissa would be permitted to be around the Dark Lord because he would consider her a useful enough person. She was not actually a Death Eater, but she served their cause in other ways, like providing them with headquarters and supporting the Death Eaters in her family.
In addition, getting rid of Narcissa would serve no useful purpose to the Dark Lord. She wasn't getting in his way, she was likely actively helping the cause, and forcing her out would likely only make the Death Eaters who are related to her upset. Bellatrix is incredibly loyal to the Dark Lord, so having Narcissa leave his presence may upset her, but it certainly would not have made her betray him. However, Lucius and Draco would probably be at least tempted to question their loyalty to the Dark Lord if he made their wife and mother leave.
Of course, this was all only until Narcissa decided that serving the Dark Lord could put her family in danger, at which point she promptly defected.
