Well, we already know this girl liked to drink. She also got busted for it more than once...so we can assume she couldn't handle it very well either. Would she have been in any shape to go to an after party or was she pretty much out of it at that point?
Parking remotely was because he wouldn't want anyone to see her get into his car at all. If he were parked around others..someone would have seen them together and have already connected him.
I think Kelly was self-medicating b/c of her grief. Also, she was a Whitewater student, and they drive much more. Very few students at UW have cars, so they don't get DUI's because they stumble home instead of driving. Kelly's DUI's were in Dane (Madison or Waunakee) and Walworth (Whitewater).
I think based on Cafeguy's story that Kelly was pretty out of it. But maybe second guy said "Come in the car and we'll go to another party..."
If Cafeguy's story is true, then second guy has less reason to avoid being seen. I don't think anyone would have thought it unusual to be getting into a car at that time of night - parked remotely or not.