The incident happened at around 10pm on Saturday 29 August in an alleyway off of Clarendon Road.
The woman reported she was in the alleyway when a man not known to her attacked her.
Detective Inspector Emma Crute said: “To able ascertain the exact circumstances of what happened, we have been conducting house to house visits and scoping CCTV in the local area. These enquiries will continue, and we would ask any residents to assist us should they have information that could help.
Anyone with information is asked to call 101 and quote 44200333243.
Alternatively, call Crimestoppers on 0800 555 111 and leave information anonymously.