Sounds like it was a series of individual votes and Christine wasn't extended the courtesy. Mick and or Stevie made the decision, ran it by John and then delivered the news to Chris. They banked on the fact she wouldn't want to leave again, totally taking advantage of her and any insecurities about being new to the band again.
Regarding Stevie talking over Chris, she's just a rude out of control egomaniac. There's not a way to say it any nicer.