Yep, guy buys the girl's corsage, she buys his boutonniere in these parts too.
OP, hopefully your daughter is wearing the same dress to both proms.
Younger DD went to two separate proms, but she HAD to get two separate dresses. Nobody other than her and her date were at both proms. Nobody would ever know she wore the same dress twice. But I was told that I "just don't understand."