What is the Shar'i ruling on a girl recovering health insurance money in her name for her sister's surgery? Did she lie to her employer, and how can she expiate that act?

What the sister did—cheating, deception, and lying—is forbidden (haram). She must perform sincere repentance by returning what she took unjustly to the responsible authority without informing them of the reason. As for what afflicted her sister, it might be due to the ill omen of the sin.