I would be willing to bet that there would be a lot more tension if the majority were forced to stop doing something than there would be if she just didn't participate.
If the 8 in the prayer circle knew how the other 3 felt, they might say, 'I never thought of it that way, I don't want to make anybody feel uncomfortable or leave my friends out. Let's find a solution to this.'
When you're on the field, you are a team. Why would a team want to do anything on the ballfield that divided you?
Rather than looking at it as majority vs. minority, I see it as the request you are making to each side. To ask a group of kids to consider not doing a prayer circle on the field before and after games, or to consider ways of making them inclusive, is a minor favor, iMO.
But to ask someone to walk away from their teammates when they are doing a prayer circle, or to participate in a prayer circle that forces them to pretend to be something they are not, is a much bigger favor to ask.