The victim, a woman in her late thirties, was walking along Rose Street when a silver BMW pulled up beside her.
The driver, a white woman, started arguing with the victim before getting out of the car and attacking her.
The victim sustained a cut above her left eye, for which she required medical treatment.
Police are appealing for witnesses to the assault - which happened at about 10am.
Anyone with information can contact PC John Finnerty via the Thames Valley Police Enquiry Centre on 101.
To remain anonymous, call Crimestoppers on 0800 555 111.