Manga about a female lead who is reincarnated into her own book

Question

It’s about a girl who got sucked or reincarnated into the book she wrote. The world is dying and she’s there to help it. She has a spirt guide to help her.

The male lead, who I think was the villain in her book, does not have a happy ending. In her book she gets to know him, falls for him, and wants to change the ending in the book she wrote. For that she needs to get back to her world which the male lead, who I think is a prince, helps her get to the castle were there was a cave that returned her to her own world.

The ending is that she gets back to her world and changes the ending of the book; she writes it so that the villain who is the male lead has a happy ending, the spirt guide that helped her through the reincarnated world visits her in the real world and helps her go back and she has a happy ending with the prince and gets married.

Answer 1

This is likely As You Wish, Prince. It is licensed by Tapas, and previously by Tappytoon (listed as expired). It is complete.

"If you wrote me, then you can give me the throne!" Yoonsoo is the successful author of a popular fantasy series. Just as she's about to start work on a new series, Imperial Prince Einzen Kyte, the worst villain she created has kidnapped her into the world of her own story?! Can she mold this nightmare into a story that will turn both their fates around?

The opening has her forcibly taken into the world of a webnovel she wrote. As in the synopsis, this is the villain emerging from a sink hole, finding her, and kidnapping her. He insists she uses her powers as a witch (i.e. the author) to fix his life and undo the abrupt favor granted to the other princes and pain given to him.

There's explicit mention that the country she's taken to is now mostly barrel, but it's not clear from skimming it if this only applies to the country or to the entire world, as in the question.

The ending is as described; she returns to her world and writes a new chapter in the series, with Einzen Kyte as the protagonist, and gives him a happy ending. Shortly after she finds the spirit animal in her apartment and is taken back to the other world and marries Kyte.

She does not immediately recognize the animal; I think it had another form during the majority of the story. A comment I saw suggests it had a more "inky" appearance, which I guess is fitting for an author. I was not able to find the spirit animal in the first ten or so chapters, so I can't confirm that it was sent by the world tree or anything.