The power that she infused into her vocals through her career is partially the reason her vocals gave away eventually.
This doesn't necessarily mean that drugs and alcohol were directly responsible for her vocal disintegration.
This is the natural aging process in all of us.
Unfortunately these superstars who reach such a notable standard as a performer have a difficult time accepting
that what they could do in their 20's is not what they can do in their 40's and 50's.
To further that problem is when for one reason or another they need to return to perform professionally and
they are confronted with their lack of their abilities they once knowingly had.