How to reproduce
1-On a survival world find a wandering trader
2-Do your best to remove the wandering llama's lead (trap the llama and make the wandering trader go far from the llama)
3-Leave and join the game.
4- Right click the llama.
5- Done! Note that you can even change her carpet, But you cannot control it
(Fourth image:My pet until she disapears :3)