I'm mad that my step mom gave my tea to my sister
What made you so mad that she gave it to her?
I was more thirsty than my sister who isn't more important than me.
I'm sorry you are feeling that way about it. You shouldn't be jealous of people. If you feel your step mom is giving her special treatment, you should discuss your concerns with her.
Huh, I was just following the rules of the house which is to go to mom when first you are thirsty. It's stupid that she gave it to my sister, who wasn't even crying about it.
Perhaps your step mom didn't realize how thirsty you were, it's an honest mistake so please don't harbor negative feelings towards your sister. If it really bothers you, why not tell your step mom about it?