I think a more likely scenario is that her parents and siblings wrote her off a long time ago.
A bunch of people signed a public "friends and family" support letter for Betty Ford a few days ago. What immediately raised a red flag was that the only family members to sign it were from her HUSBAND's family, not hers.
You are correct and I was wondering about this. It was her sister-in-law who spoke in support of her, not her sister.