The 47-year-old and an 18-year-old girl were found injured in The Nursery at 3pm yesterday (July 6).
Officers and London Ambulance Service crews attended and they were taken to hospital.
The woman sustained life-changing injuries to her abdomen, and the girl also remains in hospital.
Her condition is unknown at this stage.
Two 16-year-old girls have been arrested following an urgent search for two suspects.
One was arrested on suspicion of attempted murder.
The second was arrested on suspicion of attempted murder, possession of class A drugs and robbery.
They both remain in police custody.
Investigating officers are asking anyone with information to get in touch on 101 using crime reference number 4512/06JUL.
Alternatively, an anonymous report can be made via Crimestoppers on 0800 555 111.
