听说班主任上辈子是容嬷嬷
[tīng shuō bān zhŭ rèn shàng bèi zi shì róng mā mā]
Based on a character called 'Nanny Rong' from a popular Chinese period drama known for being strict. The name 'Our homeroom teacher must have been Nanny Rong in her previous life' suggests someone is perceived as strict or authoritative.