The incident occurred in Northney Road between 1pm and 2pm last Monday, May 1.
It was reported she had been hit a number of times in the face by a teenage boy, which officers believe has been seen by at least one person.
Officers investigating the incident are keen to speak with this person, who was driving past at the time but slowed down as they passed.
They are also keen to hear from anyone else who may have witnessed the incident and can assist their enquiries.
Anyone with information should call 101, quoting the reference 44230171026. Alternatively, you can submit information on the police website.
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