I'm going to a formal event with a girl to meet other girls.
Why do you want to meet other girls?
I'm sure if other girls meet her, they'll know what she's really like.
Going to the formal to meet other friends sounds like a good idea. If you are trying to get the girl to meet other friends then this is a very nice thing of you to do. Sometimes people just need to allow others to get to know them in order to really form a true friendship.
I'm going to romance her and make her mine.
If you keep treating her well and showing the people in your life that is a good way to go about it. You shouldn't overwhelm her and introduce her at a pace that isn't too fast though.