After analyzing everything and crap
Truly our prostitute Charlotte (her stage name) is actually Elsa.
They have same breast size and everything.
Even the ending sex quote is the same.
Plus if you go to shop on same day after you pump multiple load to Elsa, (use the pill to get your dick strong) you can still see the semen inside Charlotte's womb and she even said you the first guest (still this brothel got hella no people or something.)
Plus her feeling carry on from Charlotte to Elsa
So Elsa = Charlotte theory is right.
So why Elsa ending and Charlotte ending?
My best guess is
Elsa is her real identity where she is innocent villager.
Charlotte is her work identity where she is sex worker.
Reputation-wise she want to keep things down and not wish harm Blacksmith as in medieval-time, whore is frowned upon.
But Blacksmith logic is he's a commoner, no one cares what he does, he can marry a whore if he wants. Therefore, he does. I think Elsa know that Blacksmith broke the promise to go to brothel as she is Charlotte so this sadden her much. It could be Elsa might be keep herself for Blacksmith when her feeling level is above 5 and see no one beside Blacksmith, so she happy if he came, and drop by 5 or 3 or 4 if he didn't came.