The Sims 3: Where Have The Ghosts Gone?

I have The Sims 3 for Xbox 360. My Sim Girl has been in a boyfriend/girlfriend relationship with a premade ghost named Derek Monroe in the Moonlight Valley Specter Family Mausoleum. Everything was going great until one night. My Sim is a young adult and works at the Private Charity Warehouse (aka The Evil Headquarters). She gets off around 2 A.M. and has these traits: Kleptomaniac, Evil, Family-Orientated, and Insane. I planned for her to invite her ghost boyfriend (Derek) home and then try-for-baby together. When she ran over to the cemetery, she did not see any ghosts wandering around (like they normally do). She then went over to her boyfriend's grave and when I clicked on it, all it said was 'Remains'. I checked all the other ghosts graves and they said the same! I was freaking out! When my teenager was throwing a party around town though, she saw one of the ghosts that normally occupied the mausoleum. Now, I've seen two or three of the normal, premade ghosts walking around town, but they will not return to their gravesites and my young adult Sim can no longer visit her boyfriend so she can have a ghost baby. I've tried everything--now, what should I do? Has this happened to anyone else? Where have the premade ghosts gone? I have wondered and finally came to the conclusion that maybe I should get the young adult married, then kill her husband, and then have a ghost baby with him. Please, just can somebody help me?