This is my take...
I think Daniel was an accident. She probably needed a fix and didn't want to do it in front of Daniel so she and her sneaky conspirator put it in the cup and somehow they got mixed up. That's why she was having those dreams about Daniel. He was haunting her rump saying ...you're coming to join me...I'm in purgatory come with me mom!!
I think her death was from neglect and from everyone trying to hide her drug use. A two day coma and no one takes her to the hospital..a 105 temperature and they are giving her ice baths. Neglect.
Manslaughter at least.
If you are drunk and you kill someone - it's at least manslaughter or sometimes negligent homicide.
I cannot see where being killed by a lethal dose of drugs differs from being struck by a car.
Either way you're dead at the hands of someone under the influence.