1. Communicate and understand the situation: First, have an open dialogue with your sister. Understand why she mortgaged the house and her financial situation. Through communication, you can better understand your sister's intentions and plans.
2. Seek legal advice: Please consider consulting a professional real estate lawyer or financial adviser, who can help you sort out the issues of rights and legal liabilities, especially those related to real estate and loans.
3. Consider protecting your rights and interests: According to the local laws and the documents you signed when you transferred the property, you may still retain some rights and interests or requirements. Real estate lawyers can help you understand and protect your rights and interests.
4. Explore solutions: You can discuss possible solutions with your sister, such as finding other loans or financial institutions to replace mortgages, or finding other ways to reduce risks and explore possible repayment plans.
5. Seek family reconciliation: Family problems can be solved through frank dialogue and mutual understanding between sisters. Try to find ways of reconciliation and compromise to avoid lasting friction and disharmony. Most importantly, seeking professional advice is the key to solving such problems. Real estate lawyers or financial advisers can provide you with appropriate suggestions and solutions according to the specific situation.