There are two sides to her at the moment, she indeed works for the enemy. On the other hand she's working under false pretenses, someone has fed her lies about Rimuru... and informed of facts that shouldn't be widely known. Does he have a traitor? Clayman's machinations once again? Someone in the kingdom where he was teaching?
But even if that's forgiven, still fact remains she DOES work with the Church which is an enemy to Rimuru, but she's Japanese so we don't know how loyal she is to that creed, though at the moment she seems fairly fanatical to her God.