Police said Rajesh Kumar, 25, shot Shivani in Narangpur Jatola village on outskirts of Meerut on Monday afternoon.
As the girl lay in a pool of blood, the man smiled while looking down at her and then walked away, brandishing his pistol in the air.
The police have filed a murder case against the accused who is at large.
Shivani was rushed to a hospital, where doctors declared her dead.
Poonam Sirohi, Deputy SP (Meerut), told reporters that Shivani and Rajesh Kumar lived in the same neighbourhood and were friends.
Kumar’s marriage was fixed about a year ago and Shivani started keeping a distance from him.
“It is suspected that he was irked by that and shot her dead with a country made pistol,” said the Deputy SP.