As a teenager she would 'sneak' out (of her house/apartment) at night to visit her boyfriend.
I'm going to 'sneak' a smoke. [=I'm going to smoke a cigarette while nobody is watching]
She took a 'sneak peek' [=a secret look] at the birthday presents hidden in the closet.
(..) MARTY: The flux capacitor. It works! It works! I finally invent something that works! You bet your ass it works. We've got to sneak this back to my laboratory. We've got to get you home! This is it. DOC ON TV: DOC: Why, that's me! Look at me! (..)1985 Back to the Future