Really annoying people hate on Marie so much, few things to consider is:
1. She was always taken cared of by her big brother instead taught how to do it herself, raising her to casually use his brother because she doesn't know how to deal with her problems herself.
Apparently nobody really considered to explain her narcissistic personality even up at moment she technically killed her brother, but by then it was far too late.
She did the same in Otome World as seen with princelings and whatnot.
2. She abused the Otome World system, big deal, so does Leon, all stuff he has was supposed to be Livia's possessions as she is the mc of original game.
3. Considering Marie gone through in original world, from far too late parenting, unwanted pregnancy, parents taking her child away, abusive relationship and being bitten to death, her getting back on life while enjoying it is normal. Not like Leon doesn't try to get back on his missed out life either and enjoying to the fullest.
Yes, she is careless about her actions (albeit she didn't knew about why exactly she couldn't become mc instead of Livia, didn't play the game), narcissistic (she was raised without proper acknowledging the issue) but berating and physically abusing without constant explanation that may eventually change her is just evil.