Ok, this is denial. I’m not saying she’s doing drugs; but here’s what I did in high school.
Dad dropped me off at school. Walked into the school and out the back to the ‘smoke pit’ where at 8:30 I smoked a joint with my friends. We were all good kids without criminal records and from affluent families. I would attend 1 or 2 classes a day, many times none at all. My school also had an automated phone system, which I blocked (all 7 different lines) using *67(?). Nobody from the school could phone my house. Trust me, kids have all the time in the world to do drugs.
I would still ace all my tests. Though, that was only because high school is rather easy when you are reading university history texts for your own pleasure. Failed all my courses though because I did zero homework. Dropped out of high school my senior year, got a job, and travelled Europe that summer. Today, I’m in my last year of university, an honour student, preparing for law school next spring. While, I don’t advocate my path for everyone, I might suggest leaving her alone. Punishing her with chores and groundings will only drive her further away from you. There is a reason she isn’t doing homework. If all her friends are diligent A students, she would try to be the same.