I get what you're saying, and I think if she'd said it at any other time, she probably would have got a community sentence. But a post encouraging people to burn down a mosque when people were literally trying to burn down hotels of refugees is different from the same post a month earlier when no-one was listening. Similarly, the Islamists got such a huge punishment because it was happening at a time when Islamic terrorist attacks were a very real risk and people were out there committing acts of violence (including murder) across Europe against people who were 'insulting' Islam. When sentencing these kinds of crimes, the likelihood of someone actually doing what the person is inciting is definitely a factor, and it's undoubtedly true that people were willing to do what she was encouraging at that time.
There's also the potential defence of hyperbole to make a point, which again, slightly disappears when people are literally doing what you said they should do. If I watch Jamie Carragher on Sky and then post "someone should give him a slap" you'd be hard pushed to claim that I was genuinely inciting violence against him.