If your mother has lost important parent documents for her house, it's crucial to take specific steps. While an online police complaint might be pending, you should visit the concerned police station directly to lodge a formal FIR for the lost documents. Following this, obtain certified copies of the missing documents from the Sub-Registrar's office. It's also advisable to publish a notice in local newspapers and consult a lawyer for a suit for declaration to aid in the family settlement process.