Well, one challenge could be facing the hatred of the other characters. Since you're the villainous empress, most of the good guys would be against you, making it tough to have allies. Another is dealing with the moral implications of your actions. Even if it's in a novel world, you might struggle with the evil deeds you're supposed to do.
First, you could try to understand the character you've become more deeply. Read the novel carefully to find out the motives and actions of the original villainous empress. Maybe you can find a way to change her fate or at least make her more likable. For example, if she was originally cruel because of past traumas, you could try to heal those traumas in the story's context.
One way is to find common ground with the heroes. Instead of always being in opposition, you can work together on some issues that benefit both sides. Also, you can use your power for positive changes in the empire, like improving education or healthcare. This could start to shift your reputation from a villain to a more complex character.
You need to be very careful with your decisions. First, figure out what led to the tragic end in the original story. Was it because of a particular relationship or a political move? Once you know that, you can make different choices. Also, try to build a good reputation among the common people. They can be a powerful force in the novel. If they support you, it will be harder for your enemies to bring you down.
One major challenge could be changing the pre - determined fate in the novel. Since she is the villainous empress in the original story, she has to find a way to rewrite her destiny. Maybe she has to deal with political intrigue and backstabbing from the court officials who are loyal to the 'good' side in the original plot.
She could start by trying to make amends for her past wrongdoings. If she shows some kindness and remorse, she might be able to change how others view her.
You should expect a difficult path. You'll have to constantly assert your authority over the kingdom. There will be economic issues to deal with, like managing the treasury and ensuring the prosperity of the land. Also, there could be external threats from other kingdoms or forces. And don't forget about the moral dilemmas that come with being a 'villainous' emperor. You'll have to make choices that might seem cruel but are necessary to maintain your power.
Another challenge is maintaining her power. In a novel's world, power is often a tenuous thing. She might have to deal with political intrigue, like court factions vying for influence. She has to outwit her opponents and make shrewd decisions to keep her position as empress. Also, she may face the problem of public opinion. Even if she is villainous, she still needs some level of support from the people, or at least their fear and obedience. If she becomes too tyrannical, it could lead to uprisings.
To avoid being overthrown, you should first assess the reasons that led to the downfall of the villainous emperor in the original novel. Was it because of high taxes? Or was it due to political unrest? Once you figure that out, take the opposite actions. For example, if taxes were high, lower them. Also, try to build a strong support system among the nobles and the common people. Be fair in your judgments and don't abuse your power.