Of course, I don’t really know why. I’d have to talk to her. It sounds like pretty typical sibling junk. She’s showing you you can’t make her do something or she’s mad at you for something you may not even know you did or she’s just acting like a brat. She may be more worried about how your older sister would react so she doesn’t pull this stuff with her.
My best advice to you is to always ask politely when you want her to do something. If she doesn’t comply, find a way to joke around it. If you get into an argument, you lose. She has now made you jump up and down and turn red. Great fun. If instead you don’t let yourself get baited and turn it into a joke, you may become a pal that she will treat more respectfully. It’s worth a try anyway.
I wish you well,