I think in most cases and from what I believe, everything that happens after the moment you get sloshed should not be taken very seriously, so I personally wouldn't think about it too much. I think mentioning it to her would be a good idea rather than telling her best friend because that may or may not taint your friendship with them, or you can have a good laugh about it; depending how they take it. You could probably go and ask the girl whether or not there were feelings behind that kiss, but from what I've witnessed in most alcohol fueled shenanigans, nine out of ten times there usually isn't.
*I hope that made sense.. Usually most advice sounds good in my head but doesn't come out as well as it should
Good luck though, I'd like to hear how this turns out
