The main idea for the game is exploring the setting from the perspective of an MC who wants to stay in the new world, so regardless of whether MC (initially) thinks she's dreaming or not, she never returns to her 'home world' in any of the endings.
Additionally, MC doesn't act like a villainess in-game because there's no reason or need for her to act or pretend to be someone else (she's meeting people who never knew or interacted with the 'original villainess' at all, so she can connect with them as herself).
That said, please play the demo first (found [here]) to make sure the characters and choices presented are to your liking. The demo takes an hour to finish and consists of 20k words, which should be enough to let you know if you dislike the game or its premise.