ILC said she was on a 3 day high. We don't believe everything ILC said. We don't know if she even used illegal drugs, or unprescribed drugs, at all. There's no evidence whatsoever that she was an addict. It would be pretty hard to be an A B student with no unexcused absences AND a meth addict. If she was using meth, it was a new thing, not an addiction.
No, I'm not convinced at all that this was a drug thing. Would a meth user spend time in the woods digging graves? Doesn't fit IMO. I can see maybe using drugs the day AFTER. I mean, she'd have to be pretty stoked/excited/agitated after what she'd (allegedly) done, so maybe needed something to make it easier to act normal.