I don't know what to say for the hair. I personally would prefer a nice classy ponytail for me.
As for the boutonniere I say if it's a dance where the guy will be wearing a suit than yes a boutineere is a good idea. If it's a little more casual and they aren't wearing suits then I'd say probably a boutineere is too much.

I hope she has a great time, I'm sure she will.