Replacing character models in game

I was trying to replace Black Belle's character model (cs_famousgunslinger_05) with Sadie Adler but her character model is invisible, I then tried to replace her with Abigail and it worked fine, it doesn't seem to work with any other characters I've tried since including Karen and Hosea, so I'm guessing there are parameters in Black Belle's character model that Abigail shares that the others don't? Does anyone have more info on replacing characters in the game, like what parameters need to be met for it to work