The article gives some insight to when she presented at the Oscars, as told by her friend Michael Feinstein. Originally she was supposed to sit in a Director's chair, but due to the commotion caused by "the slap", she had to switch to a wheelchair at the last minute. Feinstein said that Minnelli was "very disappointed" about presenting in a wheelchair, and that it "ruined what should have been a glorious moment" for her.
So I'm wondering if her being upset by having to use a wheelchair was why she acted the way she did while presenting? Or perhaps there's more to the story? Maybe since her "farewell" appearance didn't go the way she wanted it to, it could cause her to deteriorate further. Although she was seen smoking at the restaurant.