Her partner Charlie Rowley, 45, who was also taken ill after being exposed to the nerve agent, is still hospitalised.
Dawn Sturgess, 44, died this month, just over a week after she was exposed to Novichok near the city of Salisbury where Russian double agent Sergei Skripal and his daughter Yulia were struck down with the same poison in March.
Police investigating the incident have so far failed to substantiate the brother's claims about the perfume bottle. Rowley was in critical condition for more than a week, but has regained consciousness.
Experts at Porton Down are attempting to determine whether the novichok that poisoned Ms Sturgess and Mr Rowley was from the same batch used in the attempted murder of the Skripals.
On Friday detectives said the fatal Novichok dose came from bottle found at Mr Rowley's Amesbury house.
Police revealed on Saturday they have retrieved over 400 "items" in the hunt for evidence, but warned the search could go on for months.
Britain has invited independent technical experts from the worldwide chemical weapons watchdog to travel to the United Kingdom early next week to independently confirm the identity of the nerve agent, the British Foreign Office said on Friday.
Assistant Commissioner Neil Basu, national lead for Counter Terrorism Policing in the United Kingdom, described the process as "painstaking and vital work".
"However, we can not guarantee that there isn't any more of the substance left, and cordons will remain in place for some considerable time".
Investigators have spoken to Mr Rowley and will speak to him again in a bid to find out how he and his partner were poisoned. "This is to allow thorough searches to continue as a precautionary measure for public safety and to assist the investigation team", he said.
That happened in Salisbury, only a few miles away from Amesbury.
Police said the two had been exposed to a "high dose" of the substance and had handled a contaminated object.
He said the discovery of the likely source of the couples' poisoning is "clearly a significant and positive development".
The British government previously blamed Russian Federation for Sergei Skripal's attempted murder, but Russian Federation denied such claims.
Public health officials said the risk of exposure to the public is low, but advised people not to pick up any odd items.