Ms Allena was pronounced dead at hospital after being found in the early hours with serious head injuries.
Detectives, who have launched a murder investigation, said Ms Allena was walking along Cranbrook Road in the direction of Gants Hill Station when she was attacked.
She died in hospital on Sunday morning after being found with serious head injuries.
A post-mortem examination revealed Ms Allena “suffered multiple serious injuries”.
No weapons are thought to have been used.
Chief Superintendent Stuart Bell, who leads the Met’s East Area basic command unit (BCU), sa: “We are keeping Zara’s family up to date with our progress and my heartfelt condolences are with them at this terrible time.”
He said Ms Allena’s loved ones are being looked after by specialist officers but added: “I cannot imagine the pain that they must be feeling right now.”
The police’s “priority is to catch the perpetrator as soon as possible”, han la til.
A cordon remains in place at the scene, close to Valentines Park, with a section of Cranbrook Road closed to the public, with only residents allowed through.
The force is urging anyone who was in the Cranbrook Road area of Ilford between 2-3am on Sunday to contact them.
Anyone with information or footage is also asked to call the major incident room on 0208 345 3715.
Alternativt, you can contact the independent charity Crimestoppers anonymously on 0800 555 111 or online at crimestoppers-uk.org.
They will never ask your name and cannot trace your call, your IP address or the device you use.