I think Beyond misread. But that's good advice for talking to a group!
I think the problem is most likely that you feel that when you're in a group, it's less personable. You're commanding a group, and it's like a performance. When it's just the girl, she knows you're zeroed in on her, so you feel like she may be judging you as you speak.
It's just like how major performers may never get stage fright, but if they're performing for their family of ten, it becomes much more personal instead of a sea of "empty" faces, so they can get freaked out.
Does this sound right?
I am getting ready to go off to basic training for the army, so any issues I have now will be beat out of me by then and I may come back with a whole new set of issues