I too am sorry for your loss. How sad that her life was so difficult. What a loss for all concerned.
Addiction is so hard to figure out.
Like you said, a long drawn out suicide. There is no one to blame.
That phone call could have been her or someone else. And it could have been for a number of different reasons. Chances are very high, even if it were from her, she wasn't ready to admit she needed immediate help or care.
I agree, she is finally at peace now. IT is profoundly sad. If you are close to her family at all, now is the time to do your best to comfort them. To comfort one another.
Sending hugs and good thoughts for peace.