Girl - Go into the hall where there are 5 doors. From left to right, I'll number them 1, 2, 3, 4 and 5. Go into room 4, and a small girl might be in room 5 next to you. If she's not, try entering room 5 and then going back into room 4.
Butler - You see the door right ahead of you when you come in? That's the dining room. Go in, and if you're lucky you'll see the ghost of an old man drifting left and finally off-screen. If you don't, keep exiting the room and going back in until you see him. I find that clicking on the statue outside the door helps make him appear.
When I first beat Gardenia, I thought "yay, I can go and see what's behind those trees in Eterna Forest" so I went and cut one down and saw the Old Chateau. I thought it was cool and went right in. I searched the rooms and found some things like the Old Gateau and the Dread Plate (when I found the plate I started having a fit about it being one of Arceus' items and how it was so amazing) and went back downstairs. I went into the dining room, and the butler showed up.
Me: WOW! A ghost!
Sister: ARGH! A ghost!
It was my sister who discovered the ghost of the little girl. She won't go back in there now. ^_^