While I'd probably use a different term, you could argue she was doomed, but it certainly had nothing to do with 'Soul Train,' or her not being 'black enough.' It had to do with the fact that she spent a good portion of the past two decades in an abusive relationship, and had developed a serious drug problem, which seems to eventually have taken her life.
I have a ton of sympathy for Whitney and her family (particularly her daughter), and understand that addiction - in all forms - is far more complicated than those on the peripheral will ever know, but this was certainly avoidable. I would argue that she was doomed if she didn't overcome her addiction, which - assuming early reports are accurate - she did not. The notion that once she started down this path she was irreversibly doomed, however, is a bit too fatalistic for me, and disproven by all those who do overcome their addictions, and subsequently live long, healthy lives.