1. Collect evidence: Make sure there is enough evidence to prove that your girlfriend swiped someone else's credit card, such as transaction records, chat records, bank statements, etc. This evidence will help to support your own report.

2. Contact the police: If the situation is serious, you can call the police and provide the police with relevant evidence and information, so that the police can intervene in the investigation. The police will conduct further investigation and handling according to relevant laws and procedures.