She has now been released on bail after questioning, with conditions that include not going to the hospital unless in an emergency.
Officers were called to the site just before 11am on Tuesday after a report that a member of staff had been stabbed.
A 21-year-old man who was arrested at the scene was later de-arrested and is no longer part of the investigation.
The worker who was injured was released from hospital on Wednesday following treatment.
The force is working closely with the hospital and has told them of this latest development.