As Blanchard points out in her answer, she's not the first teen star to speak on a hot-button issue recently. Amandla Stenberg, most well-known for playing Rue in The Hunger Games, inspired a lot of dialogue around cultural appropriation with this video that you should watch in full right now:
The kids are all right! And it's in part due to social platforms like Tumblr, where young people are actively sharing their views and research on social justice issues and politics (along with the requisite cat and Beyonce hairflip gifs, obviously).
At its best, the Internet offers the opportunity to learn anything you want to know, from how to speak a foreign language to why reverse racism is not a thing. Young people like Blanchard and Stenberg are part of a generation that is curious and has the tools to satisfy that curiosity.
And they are setting a great example: calling yourself a "feminist" or an "ally" is just a single step in the march toward becoming an empathetic, socially conscious person. From there, it's important to continue educating yourself and listening to what others have to say. It's all right to be in the dark about some issues, as long as you're open to learning more and stepping into the light.
If you want to learn more about intersectionality, the brilliant and hilarious Tracy Clayton has you covered with this assigned reading: