Amos told the Evening Standard: "Nick Hytner told me, 'Writing a musical is a glorious nightmare'. He said, 'You will have the ride of your life. But you will have to be willing to tear the structure down and write it again'."
Originally due to premiere in 2011, Hytner's words proved prophetic when the show was postponed.
"Nick said to me, ‘This musical has to be better than good. I'm not asking you to go away and dumb this down, or make it for every demographic so we can cash in. I'm telling you the opposite. Go darker, be brave," Amos revealed.
The princess of the title, played by Rosalie Craig, becomes so light with grief at the death of her mother that she floats and is locked away. But how the effect will be achieved on stage remains a mystery - it will fuse "animation, puppetry and aerial effects".
"Marianne is at the top of her game right now," said Amos. "This is her first musical and the rigour she puts on her whole creative team, I haven't seen anything like it in my life. She empowers us all to go off and create with each other, and then we come back and she oversees everything."
If it proves a hit, it's likely to follow the example of War Horse and other recent NT successes One Man, Two Guvnors and The Curious Incident of the Dog in the Night-time by transferring beyond the South Bank.
Look out for our interview with star of The Light Princess Rosalie Craig in the coming weeks!