Her partner, 45-year-old Charlie Rowley, was in critical condition, but has since regained consciousness.
"This is clearly a significant and positive development. However, we cannot guarantee that there isn't any more of the substance left and cordons will remain in place for some considerable time," Metropolitan Police Assistant Commissioner Neil Basu said in a statement.
Police are still looking into where the bottle came from and how it came to be in Rowley's house.
Further tests will be carried out to establish whether it is from the same batch that contaminated Russian ex-spy Sergei Skripal and his daughter in March.
Nearly 100 detectives from the Counter Terrorism Policing Network are investigating the case alongside Wiltshire Police, the release said.