Is the amount the company returned the right of the questioner or her sister, knowing that the sister does not want the money, claiming that she took the device instead of the money?

The money belongs to your sister because you bought the device for her, and the company refunded the price to the buyer (your sister) and gifted the device to her. Al-Buhuti said: "A gift from a seller to an agent who bought from him is appended to the contract and belongs to the principal." However, if your sister gives you the money, there is no harm in you benefiting from it.