She asked him because if Draco was still alive, she had something to fight for. She had a reason to lie to Voldemort. If Draco is alive, she needs to get into the school to see him and protect him, and helping Harry feign death was the easiest way to do that. But if Draco was already dead, she wouldn't have bothered.
When Voldemort "killed" Harry in the Forbidden Forest, she asked him whether Draco was still alive, as she knew that the only way she and Lucius could search for Draco inside Hogwarts would be as part of Voldemort's victorious army. Though she disliked Harry, she placed her family's welfare over Voldemort's goals.
Not knowing whether Draco was alive or dead, Narcissa chose to lie to the Dark Lord rather than risk losing her son. When Voldemort asked her to check if Harry was dead and she realised he was, in fact, still breathing, Narcissa seized her opportunity.
Stuck in the Death Eater camp, she had no way of knowing what was happening to Draco or even of getting in contact with anyone who knew - until Harry came along. He was the only person in that clearing who might have a chance of knowing whether Draco was alive or dead, so she took that chance and asked him.
'Is Draco alive? Is he in the castle? ' The whisper was barely audible; her lips were an inch from his ear, her head bent so low that her long hair shielded his face from the onlookers.
Pansy Parkinson
Draco lost his virginity to her on the Yule Ball night in fourth year and since then Draco and Pansy had been sexual partners.
Draco had several reasons for lying to Bellatrix, including the fact that he was never a bad person. Moreover, he no longer found working for the Dark Lord appealing and hated how Voldemort treated his family. He did not intend to harm anyone and believed Harry was the only person capable of defeating Voldemort.
Voldemort intentionally made six Horcruxes, but when he used Avada Kedavra on Harry, he unintentionally created a seventh Horcrux. Instead of dying, Lily's love for Harry created a counter 'curse' known as Sacrificial Protection and saved Harry.
Although Narcissa's motivation was to protect her family rather than go against Voldemort, the courage it took to lie to him can't be underestimated. The untruth she told him probably saved Harry's life – and sealed Voldemort's fate.
Narcissa the devoted mother
If Bellatrix managed to muster affection for anyone other than Voldemort, it was her younger sister (even at the height of the Second Wizarding War, Bellatrix and Narcissa called each other Cissy and Bella, no doubt childhood nicknames they'd given each other).
Though Narcissa may not necessarily have agreed with all of bellatrix's life decisions, and her views, she certainly loved her sister, and will have certainly mourned her death.
This nuance was lost on Lord Voldemort, who wrongly assumed Severus Snape held the Elder Wand because he was Dumbledore's killer, when in reality Draco had disarmed Dumbledore before Snape arrived on the scene, making Malfoy the wand's true new owner.
Hermione was all about logic. Harry suspected malfoy in each and every year and he was proved wrong over and over. So Hermione didn't want to believe Harry again. And malfoy was so pathetic in her eyes that she brushed off the possibility of him being a deatheater.
Draco says she suffers from a “blood malediction,” which ultimately ends up killing her the summer before Scorpius's third year. While it isn't clear that Astoria's and Nagini's conditions are the same, Draco's description of her illness seems to match up with new information from Rowling's tweets.
In fact, Lucius' own support to Voldemort is revealed to come only under some form of duress, which is likely Narcissa's Veela Allure. When Lucius turns on Voldemort due to the reveal of his Horcruxes, Narcissa divorces him, taking 75% of Malfoy's wealth with her.
Voldemort hugged Draco as an improvisation and it wasn't planned. Even Tom Felton (Draco Malfoy) was caught unaware which increased the effect. In Harry Potter style, it was like a welcome for Draco, but as Voldemort had never known love, he didn't know how to hug him very well.
Narcissa Is A Highly Skilled Witch
As we learn in the books, Narcissa is more than a capable witch and a great duelist. In fact, she was able to hold her own against both Harry and Ron, and was even not afraid to stand up to her insanely powerful and twisted sister Bellatrix.
Lucius Malfoy may be one of the Dark Lord Voldemort's Death Eaters, but that doesn't have to mean he's a bad father or that he was cruel and had hurt/abused his wife, Narcissa Black Malfoy, and son, Draco Malfoy. He's definitely an awesome and loving father.
Narcissa knew that the only way she would be permitted to enter Hogwarts, and find her son, was as part of the conquering army. She no longer cared whether Voldemort won. She didn't only want information about Draco, she wanted to get to him.
Though Harry encountered many opportunities that deemed Avada Kedavra necessary, it remains as one of the Unforgivable Curses Harry Potter never cast. For one, he viewed the spell as an immoral practice commonly used by users of the Dark Arts.
Voldemort wanted to humiliate Dumbledore, not kill him directly. Plus the story wouldn't allow it, the book would have been over so quickly. Voldemort was a dark lord that could have also been killed MANY times with the killing curse, but what story would there be if that happened?
The Death Eaters and the Dark Lord don't simply cast Avada Kedavra on everyone all the time because it doesn't suit their long-term goal of ruling the world and having a wizard-run society.
Bellatrix Lestrange Killed her own cousin, Sirius Black: She killed Sirius (who was her cousin) during the battle at the Department of Mysteries. She was remorseless and was cackling in glee after she had murdered Sirius.
Cruciatus Curse ('Crucio')
Harry tried to use this spell himself. The first time was against Bellatrix after she had killed Sirius.
Harry Potter and the Deathly Hallows
In this book, Rowling reveals that Bellatrix is the guardian of Helga Hufflepuff's cup (though she is unaware that it is a Horcrux), which Voldemort has entrusted the Lestranges to keep in their Gringotts vault.