I'm going to turn down my sisters music and give her earbuds
Why do you want to do that?
Because she can't just play music loudly without asking me first
That's right, loud music is annoying when you're busy with something else. You should tell your sister to maintain a reasonable noise level of her music.
I also don't like that she is listening with her friend instead of studying or working.
For now, I would just concentrate on your own needs and not worry about your sister.  If you can convince her to be polite and respectful with her music, then you will be able to concentrate on your work and studies.  Giving her earbuds is a great way to do that.