And I just realized that MC was conflating being love with becoming beautiful. Maybe it's cuz I've never experienced it first hand myself, but I wonder if MC actually was in love with Marie?
I think the MC inherently has a twisted idea of what love could be. Maybe she genuinely was in love with Marie, because Marie was helping her see a side of herself that she couldn't bring out before, and because Marie was the first adult in her life that seemed to actually care for her as a person. It could be true as well that she was using Marie too, she was her manic pixie dream girl for lack of a better term.
Idk how you go from being called AI cuz you only care about if smthn is good for you or not to actively acting in against what's best for you?
Well, the MC is clearly not a reliable narrator. She's so obsessed with Marie that it's clouding her judgement in everything. She already doesn't have a healthy idea of what love is, and she harbors resentment for her parents who have been neglectful all her life. It makes sense that she's apathetic to the idea of murdering her father, who she views as having torn the family apart (yes, they were both cheating, but the dad was the one who went a step further to end the family arrangement) and had the gall to try to make a new, happier life for himself in her own childhood home without her. Her hypocrisy and shortsightedness is intentional, because all these combinations of emotions without a healthy outlet are driving her to the extreme.