I would probably say for you to go ahead and go...just like you said, be cool not over protective. Make sure she knows that you're not going to "hover" over her, but that you'd like to go along for the sight seeing and that since the teachers want chaperones that you'll be going.
I don't think I'd be comfortable to allow my daughter to go and be the only girl with a bunch of boys without some adults other than teachers going. Not that you can't trust your daughter but anything could happen.