She was stabbed in the neck in front of horrified onlookers who said that her attacker rolled a cigarette as he waited for police to arrive.
The mother of two sons aged 19 and 20 worked nearby but lived in Fulham, west London.
She was taken to a hospital in central London but was pronounced dead.
Police are now appealing for witnesses who filmed the aftermath of the murder to come forward.
Detective Chief Inspector Noel McHugh said: “Ms Turner was a hard-working mother of two boys. At this early stage we believe she may have known her attacker and we are appealing for anyone with information about the incident to come forward and help with the investigation.
“In particular we would like to speak to a black male who was wearing a white tracksuit top who witnesses saw taking images at the scene.
“He is not a suspect but we urge him to get in touch with us as soon as possible.
“I would appeal to him or anyone else to contact us with the footage or images they took as a matter of urgency and not to upload them on the internet or share them with friends as it may harm our investigation.”
A 46-year-old man was arrested at the scene and is being held at a police station in north London.
GP Dr Fariba Azarian, who worked with the victim, told the Evening Standard: “She was an absolutely lovely, lovely lady. One of the most professional and caring people that I have seen.
“She was somebody who would go out of her way to help people and patients. She was very, very kind. We are just shocked and distraught by it.”
Anyone with footage, images or information can call police on 020 8785 8099 or Crimestoppers anonymously on 0800 555 111.