Narrowing down to three

[She's a new maid hired a few months ago. If I remember correctly, her name is Andrea. She has short hair and a huge scar on her arm.]

Heaven memorized the details her son had given her about the maid he met that night. This servant named Andrea was not on Heaven's suspect list. Looking back on that night, Heaven met Miriam in the mansion's lobby. 

Miriam couldn't be on the roof deck before Heaven did. Mrs. Deng wasn't in the manor at that time. It wasn't obvious, but that memory never left her mind. 

"Madam??" Heaven's train of thought halted at Miriam's call, snapping her eyes at the person across the kitchen counter. "Are you alright? You were zoning out."

The corner of Heaven's lips curled up, shaking her head. "Everything is alright. I was just thinking of something."

"Ah." Miriam smiled back, nodding in understanding. "But Madam, I think you put too much sugar in the juice."