in the first chapt she said she really came back and that she reincarnated into the villai...

Isekai, she was living in Korea

I’m pretty sure it’s isekai because she was brought into the novel. It’s just before anything had happened yet. But she hadn’t changed the time of which events happened.

It's an isekai. The events that are happening to her currently are within the novel she was travelled into, so she's basically in the early chapters of the novel, since she's read the novel she knows what's gonna happen in the future. I hope this made sense ^^

ohh okay thanks for explaing! but why does she sometimes say stuff directly showing that she time travelled like when she met sir abusive she said that he was her ex husband I'm pretty sure she doesnt have ever married before let alone have an ex husband and before that she said something along the lines of "in the past" is it just a mistranslation or like what

She said that "it hasn't happened yet" meaning that she's currently in the early stages of the novel. Remember, in her past life she finished reading the novel. Therefore she knows the ending and what's gonna happen next, like how she knew that it was her brother that poisoned her or how she isn't expecting anything from the prince because she know's he'll mostly likely love olivia (stated in the novel she read)

Actually there are many other manhwa that mix isekai and time travel

It's when FL is originally from a fantasy royal world but they died, they got reincarnated as korean girls and read a novel/play a game without knowing that the story of the novel/the game really happened in their previous life, then they got reborn as the novel/the game character and gradually remember that the character is actually their original self

Manhwa with this kind of story are : suddenly i became a princess, the villain's savior, death is the only ending for the villainess, evil lady's hero, i become the hero's mom, etc...