Do you have a cot you could sleep on that you could reposition so it blocks her doorway?

What does she say when you ask why she was sneaking out?
How dumb does she think you and her dad are?
Why does she think you object to her sneaking out?
Any community service programs you could involuntarily enroll her in, so she's too exhausted to sneak out? Maybe some program helping the handicapped, or ministering to AIDS patients, or anything that might both help other people and make her see her own life isn't so awful? "If you log x-hundred hours at community sservice, we'll let you take you license exam ..."

Hmmmm - military school? Just kidding on that one ...

What does she want to do with her life after high school?

Just saw the idea above mine: I have a rope of bells Aunt Bertha used to hang on the cellar door, in case a burgular tried to get in through the basement - wanna borrow it?