What she (and other climate activists) have done and do is spread awareness about this issue. As you can imagine, it's important to keep important topics (arguably even the most important topic humanity faces, yes even more important than soccer (lol)) present in media and in people's heads for them to not be forgotten soon after again. People need to be constantly reminded that our current way of life currently destroys our planet, especially considering that not much happened to steer against this problem within the last couple of years after the Paris agreement. And we don't even know many of the tipping points that could accelerate disaster even further. When some ecosystems stop existing and food chains become disrupted, for example.

In a way, she's like a PR person for the most important topic in science currently. And she (and other climate actrivists) is successful at it, considering it's so often in the news and so many of the polluters hate her and try to discredit her and others.

Always remember though: it's about the problem, not specific people. Of course we like talking about people, and the media does it as well, but as the saying goes, "small minds discuss people, great minds discuss ideas". It's about the problem at hand, irrelevant of Greta or other activists. She's just trying to bring the point across to a mass audience, that's all. We (as in: the whole humanity, no exceptions) need to take action against the problem, not talk about Greta. This "ad hominem" strategy is sometimes deliberately used as a distraction away from the issue at hand. When articles talk about Greta or try to discredit her or whatever, then the debate is shifted away from the actual problem at hand. Even articles about her in a positive light are, in the end, irrelevant. It's not about her, or other climate activists. She even says that herself. If the activists didn't exist, we'd still face the exact same problem.