What i did is download sim PE and followed these instructions
link (removing the i'm dead memory from Bella Goth) i went onto the sims 2 game and played onto a family where mortimer is. (I had him in the Caliente family) save before あなた use the L(デスノート) and D cheat/tombstone after entering boolprop. Click on add nieghbour to family - bella goth. Make her fall in 愛 and get married to Mortimer, and make her bestfriends with Cassandra and her brother. Play on another household, come back and Bella should be there, and she shouldn't disappear. This is what i did and it worked for me. Yes she dosen't have the memories etc but its the real Bella goth and not the one that looks different from strangetown. Plus if あなた go onto the Bella you've brought back's family tree, its correct and shows up her original children. Hope this works for you. :D