How do you get your big sister to play Littlest Pet Shop with you

Realistically, there are two possibilities. Possibly there is something that you can do for her, in exchange. Friendship is a process of mutual benefit. She does something for you, and you do something for her. But possibly there is nothing you can do for her. In that case I would just have to advise you to find someone else, who would enjoy playing Littlest Pet Shop with you.