Theory about Sophie.
I don't know if this has been addressed before, I couldn't find anything on a search.
I was watching someone play through the prologue and it struck me as odd how long it takes Sophie to gommage compared to everyone else.
But then I thought, people are being gommaged based on how old their chroma is, so Sophie must be younger than everyone else thats 33. One of the NPCs in an earlier interaction says something about it being Sophie's special day, which previously made me think about it being the day of the gommage, but now I think its refering to Sophie's birthday.
Sophie was born on gommage day. I think further evidence is people being surprised that she is 33, saying they thought she was younger. She was probably actually almost the same age as Gustave, with Maelle saying he is the oldest man in Lumiere. He was probably only a day or two younger than her.
TLDR: Sophie was born on gommage day and is probably almost the exact same age as Gustave. The reason she was the last to gommage is because her chroma was the freshest.