"Hey, GF, what did you think of this format? I want you to have fun, but I'm worried that you're not enjoying it. It also seems like there are some unspoken expectations from the others, and I think it'd be good for us to discuss them together to see if we agree with them, and then maybe take our thoughts to the group."
And then be ready to either defend your GF, as well as open to potentially leaving the group with her if the other players refuse to accommodate.
Just because you think the right solution is for your GF to increase her pacing does not mean that your GF will agree with the premise, and even if she agrees, it doesn't mean that she can achieve whatever arbitrary standard the group expects.