London Fire Brigade was called on 5 August to a blaze that damaged about two hectares of shrubland in an area known as Bedfont Pits.
The human remains were discovered a week later, and a post-mortem examination suggested they had come from a woman aged between 25 and 45.
A Metropolitan Police spokesman confirmed the remains were found by a member of the public at the site close to Bedfont Lakes Country Park.
Crimestoppers has agreed to reinstate a £20,000 reward for information that supports the investigation.
Sheen was reported missing by her family in February 2020 – two months after she was last seen.
Several people were arrested on suspicion of conspiracy to murder in 2020, but no charges were brought and the investigation remained unsolved.
Police previously said she did not have a permanent place of address, a vehicle or a bank account.