It doesn't say no drugs or alcohol were involved. I wonder if they could even get a toxicology report given the condition of her body. If she was high and fell in, that's still an accidental death and the actual cause of death is drowning, not drugs. The ME's job is to determine cause of death, not write a detailed timeline of what happened prior. In the end, her body did not indicate signs of sexual trauma or violence, so they determined this was her fuck up.

Also contrary to what tv says, it can take several months to get toxicology testing done.