The most important thing is to look at her situation, from where she sits, and consider how Shape Up could be a win-win for both the downstream teams and her definition of progress.
The phrase “relaxed pitches” is going to sound really bad to a CEO! From her perspective, probably moving forward faster is more important. “Relaxed” is not where she wants to go! The pitches should be tight and clear about what valuable thing is going to be finished by the end of that six weeks, so whoever places the bet can say “we will have moved meaningfully forward at the end of six weeks if we do this.”
I have very little information to go on from your post, but my first instinct would be to look critically at the betting table step. I suspect that step is either not happening, or there isn’t enough negotiation taking place at that step. The CEO should have someone else who understands the costs and risks of putting too much work in a cycle at the table with her so they can push and pull on each other to figure out what goes in.
If she doesn’t see the trade-offs, and she thinks she can have it all, of course she’ll ask for it all. We’d all do that! Either someone else at the betting table can bring the trade-offs to her attention, or you’ll have to wait and let the effects accumulate until the pain of trying to do it all causes a blow-up she can see.