Marley is a big sister.

I mean, she actually creates a gate that keeps Rudy away from where she is playing, complete with "No Rudys" signage. This foreshadows the inevitable tape running the length of their bedroom around the time when Marley is hanging posters of the 2019 Jonas Brothers equivalent above her bed. (Then she puts on a CROWN and declares that she is in charge.)

But if anyone else steps to her little sister, Marley is all, "Hey Guys! Share with Rudy!".