The pair, both aged 19, were arguing in Liberation Square when one of the women assaulted the other, leaving the victim with injuries to her hands, arms and head, according to the States police.
She did not need hospital treatment.
The police believe that several people filmed the incident, which happened shortly after 2am.
Anyone with information is being asked to phone the States police on 612612 or Crimestoppers on 0800 555 111.
