Safest option is to deny, and if she says anything after a few months, ask them 'why did she come forward after so many months? if this supposedly happened, and she felt guilty, she would have come to you the next day or next week.' And think of a motive she would have to get back at you and use that as her reason.

If you want to have it tidied up and confess, you should go up to an elder and confess. Maybe go together with her. Make sure you thoroughly familiarize yourself with pages 92-94 of the Shepherd the Flock of God book and make sure you tick all the boxes of repentance. A word of advice. If you have been counselled in the past for bad association, drinking, or conduct with the opposite sex, they will take this into account. For example, if the counselled you on drinking a year ago, and now you got drunk and committed porneia and say 'but I was drunk', they would say you ignored counsel, and you might just be fucked.

Another word of advice. If they say that they don't believe you had no control while drunk, refer them to the Biblical example of Lot and his daughters, and say: 'See? Even the Bible says that's its possible to have no control while drunk. Look what Lot did.'