I can't believe what my future SIL wore for the bridal shower.
Did she wear something that was provocative?
I believe that bridal shower is an event where guests wear nice clothes and she didn't.
It's too bad that she didn't dress more appropriately for the bridal shower. Maybe she didn't understand how she should dress? Maybe you can talk to her and explain what the expectations are for an event like that?
She should have wore formal clothing since she knows how I expected everybody to dress.
She may not have really understood how to dress. Mistakes happen and she probably didn't mean any harm by her actions. If you speak to her, try to be gentle with your words.