First, try not to overreact. It might be that she's using it as a form of escapism. You can gently introduce other types of reading materials that you both can enjoy together, like classic novels or interesting non - fiction books. This way, you can shift her focus in a positive and inclusive way.
If your wife reads dirty stories, it's important to approach the situation with understanding. Everyone has different interests. You could share your own concerns in a non - judgmental way, for example, you might be worried about how it could affect your relationship or family values. At the same time, listen to her perspective as well. Maybe she finds these stories a way to relax, but together you can find a compromise that respects both of your feelings and beliefs.
You could have an open and honest conversation with her about how you feel. Maybe she is just exploring some fictional content out of curiosity, and discussing it can clarify boundaries and your mutual values.