Ouji-sama nado Irimasen! Wakiyaku no Kanemochi Akujo ni Tensei Shiteita node, Konse de wa Zeitaku Zanmai ni Sugoshimasu

The self-centered marchioness, Rosa Kreutzers, is injured after being kicked by a horse on the way home from the theater with Prince Alex. But in that moment, Rosa realizes something significant: "This is the world from the manga I read in my past life! And I'm a minor villainous character destin...

Source: MyAnimeList