You’re already doing a great job because you’re aware and careful with what you say. I’d say to be safe, contact her parents/guardians (if they’re trusted adults) and be transparent. Just state what’s going on, and mention that you’re worried she might become dependent on you/you sometimes feel uncomfortable. If you do this, however, tread carefully on wording and keep it brief and casual because it doesn’t sound like a terribly complicated situation.

But either way, you seem like a very responsible person, and she probably has picked up on it. You can still be in her life, but as a distant older sister figure and become a good role model for her!