her intentions may be good. she might be "just friends" with those guys, you never know for sure if there is any history or feelings with her towards on of them or one of them towards her.
The good news with her being the only girl is the guys would probably protect her and keep the other dudes away....
however, if she is ever going to cheat on you, it would be on that trip. She will be drunk, with millions of other drunk people, 99.9% of the guys there are looking to get laid, even the guys she will be with. Guys will be grabbing on her, trying to get her to show her tits, buying her drinks, grinding against her in the street etc... Then she goes back to a hotel room after all of that and shares a bed with a bunch of "drunk" guy friends who are all horned up looking at tits all night. If just one of those guys has a thing for her, and maybe she was always attracted to him but nothing ever happened... they both drunk, etc... you know what is going to happen. It just takes a little alcohol and opps... did we do that last night...
If you can really trust her to be honest with you and she doesn't cheat, then marry that girl.
I would say better than 50% chance she will at least kiss, fool around or worse. And a 90% if she fooled around but didn't have sex she wont tell you about it.
Have fun thinking about what she is doing 24/7 while she is gone. The party really is 24/7 none stop. Do yourself a favor, get off of work and go. Have a good time and don't beat yourself up worry while she is gone.... which you should be worrying.
I grew up in new orleans, went to mardi gras / french quarter every year from 16-24... trust me. either go or worry your ass off that you have an angel of a girl friend.