The alleged incident took place at the junction of Hilary Street and Hilgrove Street at about 1 am this morning.
Police have already arrested a 28-year-old man, who is currently in custody.
He was arrested on suspicion of sexual assault, and the victim is being supported by specially-trained Sexual Offences Liaison Officers.
A statement from the police said: “Police are appealing for anyone in the area, who may have seen or heard something, to contact them on 612200 or Crimestoppers anonymously on 0800 555111.
“A 28-year-old man is currently in custody, arrested on suspicion of sexual assault.”