The "Green Light" singer also insisted it helps to have a "pretty close" connection with her family who keep her grounded, which Billie also has.
She added: "Obviously she's pretty close with her family, as am I, which I think is really helpful at that age when your world is changing.
"Yeah, I mean the music is awesome. She's just doing such a good job."
Meanwhile, Eilish recently hit out at the public perception of her, as she insisted people don't know anything about her.
She said: "Anytime I see an impression on the internet, it just reminds me how little the internet knows about me. Like, I really don't share s***.
"I have such a loud personality that makes people feel like they know everything about me and they literally don't at all … that I can sing.
"That I'm a woman. That I have a personality."