My little sister is SOOO mean to me? Please please help?!?

I think you should learn to ignore her which is probably tough. And I'd say your Dad's giving you a compliment. He's saying that you are no longer growing up in the same way your sister is so don't compare your current self to her. Also, while it's impressive that you have attempted to take on the mother role, I don't think you can expect your sister to see you that way.