Wow, what is with some of these grandparents?? There are plenty of variations- gran, nana, granny (surname)... She already has someone to call her mom. Jesus. Her time is over. You're the mom.
I would enroll her a homeschool student, and have her do something academic, but it can be something that's fun for her and reasonable for you. That way when you return your ducks are in a row and there's no question that she's ready to move on to sixth.
Focusing on something you do together is the best you can do. It doesn’t matter if it’s running, playing an instrument, whatever. Encourage her. Spend time with her