My best friend stole my song?

So I wrote this song and my best friend basically claimed it as her own because she was there when I wrote it. She played it with her band and had me sing backup vocals, and the got all the credit for the song. Everyone was saying how she should write all the songs for the band from now on. I’d like to see her try to write songs like the one I did.

But what am I supposed to do?

Let it go? Because I really do care about having her as my friend.

Or do I say something?