I'm going to ask my girlfriend not to tailgate on the highway
Why don't you want her to tailgate?
It's dangerous.
It's good of you to make her not tailgate people especially on the highway. This is very dangerous because if the driver in front needs to brake hard, she will smash into the back of their vehicle.
The world would be a better place without tailgating. I'm going to tell her about this
That's good of you to do. Your concern about keeping her from doing dangerous activities is admirable.