Welcome back, Denise!
Wow, this question really sent me across the galaxy searching for an answer for you.
To have the best chance against the First Order on
Star Wars: Rise of the Resistance you will need to bring every member of your party that meets the height requirement.
You are correct that a minor's plans can not be shared through
My Disney Experience.
When you go to get your
Boarding Group at 7:00 am on the morning of your visit, the system will automatically link anyone in your
Family & Friends list that has a valid Disney Park Pass system reservation for Disney's Hollywood Studios on that day. If you are doing this from anyone else's account but yours, your young Padawan will not show up.
Denise, you have two options:
Your first option, and what I recommend, is to be the person for your party to snag your Boarding Group the morning of. To help make sure that you get a coveted spot, I recommend that you are off wi-fi in an area with great reception and that you close out all other apps on your phone before logging into the
My Disney Experience Mobile App a few minutes before 7:00 am.
Your second option is to have someone else get your Boarding Group and to visit Guest Relations once you arrive to see if you can have your youngest added to your Boarding Group. I have heard that many people have had success with this method, although it is not guaranteed.
I wish you the best of luck battling the First Order, Denise.
May the force be with you!
Sarah B.