I think you guys are making a few too many assumptions about my household. We've never ever ever had problems with our cats being violent or aggressive. We're putting the cricket toy away at night so the cats won't have that to make noise with when my stepdaughter is sleeping. That should take care of that particular problem.
My question is about cosleeping at her age when she has never coslept before. I understand that cosleeping for newborns and infants can be beneficial to the parent-child relationship, but are there any negative effects on starting this at age 6? I would prefer not to have her in bed with us at night out of comfort, but if it would be better for her when she's scared and if there wouldn't be any longterm negative effects, then obviously I would allow it for her.