It might be considered accidental because her intent was not to commit suicide. She was just inured on her drug use to the point where the amount she had to take to get high was too high for her body to tolerate in her state of health.
Same way that booze does this— to the penultimate last drink. An example of this was great country singer Keith Whitley (who never thought he was good enough apparently), drank himself to death to the point that he went to his childhood home where his momma still lived and kept his teenage years bedroom all made up for him.
He went there out of his mind drunk, and then flopped on his bed in his kid bedroom had one more hard liquor drink, and his liver had reached top of tolerance.. and he died right there. Sick, and sad.