I know it's fun to hate on the big tech companies recently and act like they are bullies (and indeed in many ways they are), but this is a bad example of that. Most companies I know of would outright fire you if you, against explicit company policy, went to the press and started badmouthing your employer. The fact that Amazon only gave her a warning is the only surprising thing in this article.
Why? There are many avenues for change, why limit yourself to just quitting? People are more than just workers and consumers.
Then again, if they choose to stay and their contract says they aren't allowed to do this (assuming its reasonable), then they should also accept it when they get fired and move along.