Do you need to call the police if your sister uses her credit card? You should:

1. Collect evidence: Collect relevant evidence as much as possible, such as bill records, transaction details, bank statements, etc., to prove Unauthorized use of credit card.

2. Contact the bank: Report the problem to the credit card issuing bank, explain the situation to them, and provide any available evidence. The bank will investigate and take appropriate action in accordance with relevant regulations and procedures.