Police said the cremation was done after a post-mortem.
The US Embassy had asked the police to preserve the body till the relatives of the woman were contacted. But there was no response from her relatives.
Willinger met autorickshaw driver Bunty Sharma (32) when she visited Agra in July last year. They got married in a court on October 11 and started living together in Shaheed Nagar Colony of the city, police said.
On February 20, Bunty took Arianne out in his autorickshaw to Tucker Road. After reaching a lonely spot, he attacked her with a knife, killing her on the spot. He later threw the body on the roadside and went back to his room and committed suicide by setting himself on fire.
Bunty's body had been handed over to his relatives, police said.