From what I've read, her room was littered with prescribition pills/tubs and she apparently mixed these pills with alcohol which reacted and acted like a seditive - she was found in the bath, drowned. So assuming the pills+alcohol did make a seditive, it's most likely she felt tired, went for a bath before bed but accidently dossed off and slipped under the water.
- Sorta suicide, but not intentionally, I think it's called homocide? "Death by misadventure"

It takes a pretty powerful sedative to overcome the body's reaction to being unable to breathe, though: that's an instinct that's very strong and will generally override almost any amount of sedation. Things like barbiturates and morphine can put the body into such a degree of sedation, but from what I understand, even when mixed with alcohol, the likes of Xanax (which she was reported to have been taking) shouldn't be able to do that.

It svcks that both her and Michael died just after making a comeback.

She took meds for depression no doubt. But I don't think she would commit suicide.

That was just one theory I heard, and it seemed pretty sound. But since it's a theory and I know nothing about the situation I'm not gonnae try defend the thing any further besides saying it seems the most plausible.
- She could have OD'd in the bath so she was dead before "falling asleep"