It was unexpected, so I'm going with heart attack or accidental od. She had a lot of back trouble, perhaps she got into trouble that way. Seemed like a nice person.
That song "Zombie" is ruined for me though. It was popular around the time Dahmer died here in the States, and became the basis for a slightly popular parody song here. That lyric that goes "What's in your head? Zombie, zombie, zombie." became "They crushed your head, Jeffrey, Jeffrey, Jeffrey."