The woman is alleged to have been assaulted by another woman outside the Randy Paddle at around 02:15 on Sunday 13 December.
Police are appealing for information from witnesses who saw what happened and can help the investigation.
Anyone with information is asked to contact PC 177 Le Galloudec on 725111. Alternatively, people can call Crimestoppers anonymously on 0800 555 111.
Pictured: Police say the incident happened outside the Randy Paddle in the early hours of Sunday 13 December.