The 30-year-old was followed into the bathroom by a man she didn’t know and attacked after he forced his way into her cubicle.
She was attending an office Christmas party with work colleagues when the attack happened in the early hours of last Saturday.
Gardai have launched a massive investigation and are trawling through CCTV in a bid to identify the rapist.
The hotel was busy at the time of the rape, hosting a number of festive functions on Friday night and into the early hours of Saturday.
The victim has made a statement detailing how she was attacked in the ladies toilet of the hotel, which cannot be named for legal reasons.She had left her friends to go to the bathroom when the man struck.
The rapist is reported to have forced his way into the toilet cubicle where he subjected the woman to a savage attack.
The victim was treated at the Sexual Assault Unit at the Rotunda Hospital.
No arrests have been made in the case and it is being investigated by gardai.
CCTV is being trawled through as officers try to hunt the sex attacker, who was unknown to the victim.
It is understood that investigating officers have used a system called VICLAS, the Violent Crime Linkage Analysis System, a computer developed by the Royal Canadian Mounted Police in the early 1990s to compare different crimes for similarities. However it failed to link the sex attack with any other similar crime.
Sources say that last weekend's incident is not linked to a horrific rape in west Dublin in which a young woman was attacked with an implement in October.
That victim - a foreign national aged 25 - was left in fear for her life during the sickening hour-long ordeal when she was targeted by a stranger.
The traumatised woman required hospital treatment for extensive injuries after the disturbing incident, which occurred while the victim was on her way home after a night out.
Anyone with information about either rape should call garda confidential phone number on 1800 666 111.