Complex sentence: Belle shows up and says she's been keeping a secret from them, but decides to tell Elsa and Emma about what happened to Anna and the fact that Sarah captured her, but that she doesn't know where Anna is now.
Split into simpler sentences: Belle shows up and says she's been keeping a secret from them. She decides to tell Elsa and Emma about what happened to Anna and the fact that Sarah captured her, but that she doesn't know where Anna is now.