Online, writing in all caps is considered shouting and from an etiquette point of view you really shouldn't do it. If you're a professional writing an instructional memo for your coworkers, there's really no reason why you would do it in all caps.
Without knowing more, I would jump to the conclusion that while her writing style may have been the excuse for firing her, I'm sure there must have been more to the story. It would probably have been a situation where coworkers had complained before and managers felt they needed to do something.
Actually on reading the article, I see that she successfully filed suit against the company. It does sound like her coworkers had complained in the past, but since they hadn't documented and spoken to her about it before firing her for "creating disharmony", the company lost it's case.
Any one interested can read more on it here: