Haunted House in Convent

This is a story by my sister where her school, Main Convent held an event...let me recall...i think its a Canteen Day. They even made a Haunted House by connecting a few classrooms to become a single big room and this is the spot for the Haunted House. On the Canteen Day, those who wish to visit this Haunted House may take a walk in it. They have already allocate girls to become 'ghosts'. Many people went to visit this house and one girl claim to have seen a ghost. She told the rest that when she was visiting the house, she saw a lady who is unfamiliar and she was wearing yellow dress in the house. The way she described the lady made them more horrified as none of them recognise this yellow dress lady.