A group of three people that hang out together a lot. Used in specific terms, it is often preceded by another word or words to distinguish it from other handles.
Just like somebody who's not straight shouldn't be trying to set everyone else straight, someone who has enough trouble controlling their own actions and handling themself doesn't need to trying to handle other people.
The girl wanted to look like the one who could handle anything and anyone to the world even though some people had seen her lack of control over quite a few of her own actions in life.