If you get on with her you could ask whether her yelling scares the shit out of her kid because it’s loud enough to wake you.
I’m pretty loud by nature (people in my office often remark) and I was inclined to yell at my kids because I didn’t believe in physical punishment. One day I saw my son about to hit his little brother and yelled at him. The kids had no idea I’d enterred the room and my yelling terrified both of them to tears. After seeing the looks on their faces (Wes Craven eat your heart out) I greatly toned down the volume.