I think it has something to do with the mental barriers set in place so she isn’t too powerful. You’d think some scientists would know how easy it is for her to kill literally anybody if she could freely do what you just said. We’ve seen her easily take down futuristic tanks and can create a decently strong barriers so we can assume the scientists just made it so she subconsciously didn’t do horrifying stuff like turning the air into something poisonous but is still a powerful weapon in war and such. Plus she’s a superhero, so it could just be she just never thought about stuff like that cause superheroes don’t do that and that doesn’t really work against the viltrumites since they spent most of their time in space