I strongly suspect that this was a case of bathroom cocaine use and not a sex think. Hey, she's got nose like a Hoover vacuum cleaner.
I doubt they would have both gone into the same stall to snort coke since it would be more likely (obviously it did) to attract attention. Just my guess, though.
You may be right. I have seen it in clubs. They go in a stall together and the one cuts out the lines, and they get high.