I say if it was initiated by the girl and you immediately stopped then I would consider it a non issue and no need to tell your girlfriend. There was no intent on your part. However, I would take caution in putting yourself in situations like that in the future. If your girlfriend has trust issues then you being around drunk girls will not help alleviate her issues. Bad things happen when people are intoxicated.
No changes in my response. It was a shocking reaction. You handled it appropriately. Time to put it behind you.