Small but disgusting tidbit here. If you have been drinking all day your pee will essentially be water and won't have a smell. During college I had a friend sleep over and I woke up to a wet spot on the carpet. Soaked it up, smelled it thinking he pissed my carpet, no smell so I figured he spilled a glass of water. It was urine, determined by the fact that he had a history of peeing anywhere but a toilet after drinking.

Also passing out after you stop drinking for a period of time is common. I think your instincts are right in that she went on this trip with an expectation of meeting up with this guy and possible hooking up, which possibly happened. In my own experience with my wife, there have been many times were we were hot and heavy while we were out drinking. Took a cab home and by the time we get there either she, myself, or both are passing out. So its possible she is telling the truth in that no sex happened, but her making out, expectation of a hook up, etc are just as bad if not worst.