The conclusion is,
She is having tea by herself, talking by herself that why the mother of the prince say that she crazy, it mean that The Real Lucia is Inside The body Of reincarnator. 2 soul in 1 body it mean
You know the real tragedy of all this, is that Lucia herself seems like a genuinely sweet friend in the flashback. If it weren't for her obsession with the harem ending, I wonder if she would've become a lovely young lady.