The media may be painting her as such, but this is absolutely not true. Keep in mind, MLK was an actual socialist who openly advocated civil disobedience and dismantling the systemic racism that is enabled by capitalism. Greta is nothing like this at all; comparing her in any way to MLK is a complete insult to MLK.
Extinction Rebellion is about as much of a liberal pseudo-anarchist movement as you can get. They actually came to prominence because they would get on top of trains, block highways, etc., to stop people from going to work just to protest, thus literally putting hundreds if not thousands of people at risk of losing their jobs. Not exactly a proletarian movement if you ask me.