Hello , I have a older brother , since childhood we both always fought, till this day we are not close as others , we ofc stopped fighting and grew up from it , but whenever we both meet at vacations at our home , I've noticed my behaviour, im always making his fun, mocking him , or try to act better than him , show him down , I think this is the reason we both have such relationship, but yes I do respect him alot , he's better than me in every aspect, I'm not jealous but proud of him, but yes I aslo don't show that bc I'm that cocky , the point is , if she's your younger sister, she will actually like this but she doesn't mean it , and it's common trait.
I can say this of my recent experience, i never had sister but there was a junior who was so close to me we were like siblings, she used to act same towards me as we grew closer. That's when I noticed such behaviour in me aswell around my brother , so yes , all siblings are like this , they don't mean it , but it's kind of a humour or trait of younger ones being annoying and disrespectful