The first adjective that comes to mind to describe Connie is "vain."  She is aware that she is pretty, and, despite her mother's admonition to "stop gawking at yourself,"  Connie has a habit of looking into mirrors to check her appearance. She knows she is pretty, "and that was everything" in her mind. When Arnold Friend turns up at her house and her family is away, Connie's first thought is about "how bad she looks" because she has just washed her hair. 

Another adjective that describes Connie accurately is "naive." She is so engrossed in her vanity, sneaking around with boys when she is supposed to be with her friends, and listening to rock and roll music that she seriously underestimates the threat that Arnold Friend represents until it is too late.  As Connie studies Arnold Friend from the other side of the screen door, she notices his tight jeans and shirt, greasy leather jacket, muscled body, and the fact that he is listening to the same radio station as she is. She remembers flirting with him at the drive-in restaurant. Connie's naïveté about the danger of Arnold Friend is expressed in the line: "but all these things did not come together."  Her inexperience and self-absorption do not allow her to recognize Arnold Friend as a predator until it is too late.