Complex sentence: At first, she was opposed by the other members of the Trinity Seven because she infiltrated the forbidden library, which is the'eternal library', and obtained the Demon Lord element sealed in the library to become the Demon Lord candidate.
Split into simpler sentences: At first, she was opposed by the other members of the Trinity Seven because she infiltrated the forbidden library, which is the'eternal library'. She obtained the Demon Lord element sealed in the library to become the Demon Lord candidate.