Update - found on 14th August.
Fortunately her owner had sensibly got her neutered and microchipped. (Hopefully owner has contacted microchip company and checked that they have owner's correct contact details). Any vet will scan a found cat for free to check if microchipped so that owner can be contacted.
Her owner has put details on Animal Search
Animal Rescue charities like The Scratching Post recommend that it's vital for cats to be neutered and microchipped. Adult cats enjoy catflap access to a back garden - and cats need a catflap access to get back inside their home. They advise locking the catflap at night so that cats are safe inside at night as it reduces the risk of them getting lost or injured.