Answer: I Don't Know.
Back in the 70's my brother was big into FM. I inherited his vinyl albums of Fleetwood Mac and Rumours. Two years ago, I listened to them again and was hooked. So I decided to buy some of the newer stuff (i.e. anything that came after 1978.)
Before I buy a book or CD I go to Amazon.com and read the reviews.
I was surprised to see this one posted:
THINGS DON'T NECESSARILY GO BETTER WITH COKE, April 12, 2005
Reviewer: Crabby Apple Mick Lee (INDIANAPOLIS, IN USA)
It was a review of ENCHANTED - The 3 CD set.
I then began to read the reviews of Bella Donna, The Wild Heart, Rock A Little and by the time I got to Street Angel, the magic in the reviews seemed to be gone, but she wasn't.
She did produce Enchanted (my favorite) and Trouble in Shangri La - but by that time her voice appeared (to the reviewers) to be more nasal and not the sweet-young-country girl sound.
Then I read where Stevie did an interview and drew two noses. One nose was hers and the other was Christine's. She drew holes (due to Cocaine use) - and hers was much larger than Christine's. She supposedly told the interviewer that she could have surgery to fix the hole, but then her voice would not sound the same, and she could not do that to her fans.
I am sure that this doesn't answer your question, but reading the reviews and then going to the local library to read old magazine articles, it appeared that the music was a reflection of what was/was not going on in her life.
One last tidbit - the morning radio DJ's (yes, they are obnoxious) had a heyday recently with some article? quote? from Stevie about Lindsay Lohan and Britney Spears. They were laughing about "Stevie's behavior back in the cocaine days" and said she was the last person to be giving advice, etc. etc.
So, to answer you question: Who knows? I don't.