Lexi, you did the right thing. She wants to hear that she's right, and she's not. Even if she were, you're entitled to your opinion, and she asked for it. Most people do not respond well to being bossed around; you're just telling her what she should expect. If she doesn't like it, she should change it. Otherwise, she should accept this is how it will be.

She might be the eldest or an older sister; often, older siblings tend to be bossy towards other ones, and they extend that into their lives, sometimes. It's not always the case, but it might be why she's bossy.