Just to be clear, Hae didn't have any illegal drugs in her system at the time she died. I am guessing she probably rarely or never smoked weed, but happened to have friends that did. Very common in high school. Even if my theory is right, Hae was just being a typical teenage girl, trying to impress the boy she was infatuated with by getting weed. I don't think for a second she was getting it for herself.
Speaking of whom...he was actually a man, not a boy, since he was a couple of years older than her. I don't get the idea that he had anything to do with her death, but I do find it strange that he was supposed to meet her after work at 10 pm and didn't seem very concerned when she turned up missing. He didn't call the investigating police officer back until 1 am. He also never paged her again after that day, which a lot of people say is something that makes Adnan look guilty (because he never paged her either). But it's more strange that Don didn't page her, because he had no way of getting info about Hae whereas Adnan did, because of all their mutual friends.
Although, he eventually became friends with Hae's friend Debbie. In one of Debbie's interviews she said she talked to Don on the phone for SEVEN hours one night!
Recently on reddit, Hae's brother Yung Lee posted that the computer had been returned to the family after the investigation, so it wasn't missing as previously thought. I'm not sure where the "lost computer" info came from in the first place, but it was wrong, so he put the rumor to rest. He has only posted a couple of other times, one of which was about the broken turn signal and/or wiper lever in the car. He is a verified poster there, I believe.
There's been speculation that Has may have kept diary entries on a floppy disk, but Yung Lee said he doesn't think she did, since they had to share the computer. However, that leaves some trial info unsourced, because Kathleen Murphy quoted something as being from Hae's diary that wasn't in her written diary. I'd have to look it up for more specifics, however, because I don't recall what it was.