We see in Harry Potter and the Deathly Hallows, after Voldemort tries to kill Harry that he sends Narcissa Malfoy to check if Harry was dead or not:
“You,” said Voldemort, and there was a bang and a small shriek of pain. “Examine him. Tell me whether he is dead.”
Harry Potter and the Deathly Hallows
Did Voldemort have any specific reason for doing this? Of all the Death Eaters, why choose Narcissa? She wasn't even Voldemort's most devoted follower, who would have given a more reliable result!
Moments earlier, Voldemort's killing curse had failed to work properly against Harry, again. It knocked Voldemort to the ground, in full view of many of Voldemort's supporters, and Bellatrix had the nerve to repeatedly suggest that Voldemort was so weakened and injured that he was in need of help.
Voldemort had to regain control of the situation quickly. He distracted Bellatrix — stopping her public acknowledgement of his weakened condition, and punishing her for her insolence — by blasting her sister Narcissa, perhaps the only person in the world for whom Bellatrix felt genuine unambitious love and empathy.
Voldemort needed for someone to check Harry, and this provided a convenient excuse for Voldemort to hurt Narcissa. Voldemort sensibly did not attack Bellatrix directly; she was too powerful and aggressive and might have fought back.
Why exactly the Dark Lord sent Narcissa, rather than anyone else, to check if Harry was alive is never made clear. All that’s seen about his method of choosing is that he hits someone with a spell and orders them to verify if Harry is truly dead.
“You,’ said Voldemort, and there was a bang and a small shriek of pain. ‘Examine him. Tell me whether he is dead.’
Harry did not know who had been sent to verify. He could only lie there, with his heart thumping traitorously, and wait to be examined, but at the same time noting, small comfort though it was, that Voldemort was wary of approaching him, that Voldemort suspected that all had not gone to plan …”
- Harry Potter and the Deathly Hallows, Chapter 36 (The Flaw in the Plan)
It isn’t made clear if the Dark Lord actually aimed his spell at Narcissa, or if he was using it as a way of random selection. If he did aim his spell intentionally at Narcissa, it’s still not clear what his thought process was behind choosing her. There’s no obvious reason why he’d choose her over everyone else, nor are his thoughts behind any choice explained in the text - it’s not even clear he made one. If the spell was a method of randomly selecting who would verify Harry’s death, then the answer is simple - his spell happened to hit Narcissa, deciding she’d be the one to check if Harry was dead.
I found this answer on movies.stackexchange.com which explains it pretty well! I didn't realize, at first, that this had already been asked on Movies & TV SE!
Some important notes from it are:
Narcissa is a very valuable person for Voldemort, although the Malfoys fell into miscredit earlier in the book. It is shown at the beginning of Deathly Hollows [Hallows], how valuable she was:
[...]
And she helped identifying Harry (though indirectly) when he got caught and brought to Malfoy Manor:
[...]
But the decision whom to send to check in the end does not seem to be rational at all:
[...]
He might have probably -subconsciously- wanted a mother to check as a mother gave the protection to Harry (but he didn't know at that point). Or he just wanted to punish someone and Narcissa was the unlucky one to stand near him, we never learn to know the real reason.
The answer-poster, @TorstenLink, also provided several quotes from the Harry Potter books to back up the claims listed above, so I suggest you check it out!
