I agree with ktsnake.
For some girls, guys are really the best friends. Me for example, while I have plenty of female friends, my guy friends are really my best friends. I don't know why it always works out that way, but it just does. And it's funny that you mention that she grew up with her guy friends, because that is the exact same scenario for me.
Unless it looks like she is seriously going to make a move on her guy friends, I wouldn't worry about it and just trust her.
I hope that helps & the situation works out for the best
