It is alleged that a man was walking past the woman on the stairs as she was targeted on December 6 last year at 5.20pm.
Police are now investigating the incident and an appeal has been launched for anyone with information to come forward.
An image of a man in connection with the incident has been released, as officers believe he may have information that would help their investigation.
Anyone who recognises him is asked to contact British Transport Police by texting 61016 or by calling 0800 40 50 40, quoting reference 468 of 6 December.
You can also contact Crimestoppers anonymously on 0800 555 111.
