On behalf of my 12 year old daughter:
My sister and I LARP with a friend based on different shows we watch (Glitter Force, Sailor Moon, and others). We have a lot of fun coming up with different scenarios and games, but most of the time our friend kind of takes over the game.
For instance, I came up with some character names. I told our friend about it and the universe I made up. My character was the Queen warrior and my sister and our friend were my warrior princesses, and we all had our own planets.
Then she used similar character names in our next game, but her character was all powerful, and our characters not only did not have their own planets, but we had to pull her around in a wagon.
I felt really hurt about her taking my character names and making up story lines that wouldn't be in line with how I designed my character - enough so that I talked to my parents about it and our parents moderated a discussion with us. She agreed to come up with her own characters, and I thought it was over, but then the next morning she came to me in private and said, "Oh, by the way, I came up with this other character months ago and her name was actually your character name so really I came up with it before you."
I like spending time with my friend and playing these games with her and coming up with new story lines but it's really frustrating when she takes over my stories, alters my characters, and makes her characters super powerful and our characters super weak.
We both have really strong leader-type personalities, so we both have pretty strong opinions. She's also an only child, so she's used to getting her way.
How can we make it so our games are fun for all of us?