I think it has to do with her getting clubbed with a rusty sword last chapter. By comparison it's nothing lolvery funny for her to say the guillotine is completely painless when in chapter one she specifically calls out how it's super painful and not humane at all. She's either gotten used to it, or that tranquilizer poison was still dulling the senses when she got beheaded this time.
She said she saw it in her dream. Why wouldn't you believe her?Executing a top ranked member of your ruling class because "I saw it in a dream"...
Okay, but how did she convince the others to help her?