Can I ride my horse in defiance of my sister, who told me not to?
Is there a reason you're doing this?
She never mind her own business, and she doesn't like it when I mount her horse without permission.
As long as you are riding safely, and have your parents' permission, there should be no problem with you riding your own horse. Your sister should not be trying to dictate your behavior like this.
Yeah, my sister is just a little kid and she has no control over me.
That's good to hear. Even if your sister was older than you, she still shouldn't be able to dictate what you do. Maybe she will learn from this situation.