Maybe I missed some things or they flew over my head, but it sounded to me like the "original novel" that the FMC read in her past life was a pretty shitty story to begin with:
If the 'villainess' was the novel's protagonist, she was torn away from her childhood friend who she had actual feelings for to be engaged to a turbo-asshole, who later takes in another lover, accuses her of stuff she didn't do, and forcibly cuts her hair short. Then her childhood friend is killed by assassins in retaliation for murdering her fiance.
If the prince's lover (traditional FMC in these otome stories) was the novel's protagonist, she falls in love with a turbo-asshole who secretly kils her cat to blame on someone else, and helps him frame his innocent fiance. Afterwards the prince she loves is murdered after the condemnation event.
Seems like neither of them get a happy ending in the original story.