Answer:
Inside the narrator's room. She was locked in by her grandma.
Step-by-step explanation:
"Dress of White Silk" is a story written by Richard Matheson. The story centers on the white silk dress of the narrator's deceased mother. Her grandmother secures the white dress inside a box with a key all the time. However, the narrator really loved that dress and how silky it was that there were times she'd open the box without her grandma knowing. One day, when her friend, Mary Jane, visited her house for lunch, she was bullied for being a liar and not having a real mother. To prove that she had one, the narrator went to her mother's room and opened the box where her mother's silk dress was. However, something terrible happened and her grandma took her away from the room while screaming, "It's happened." This became the reason why her grandma locked her inside her own room.