I'm going to make my wife shower with the window wide open
Why would you tell her to shower with the window open?
It's because I know there are girls waiting outside to have a peek at her
Making your wife to show herself naked to the girls outside isn't proper. Leave your wife alone and don't try to push her into doing things that could create trouble.
What's the big deal? I'm not forcing her to do anything since she already does it.
It's really weird that you want these girls outside to see your wife naked though. She may be embarrassed and weirded out by it.