Wow, that was sweet of your Mother to do for your sister. There are probably about a million reason she had to do that. Maybe she wanted to say, "You're still my baby"!
I had two stuffed toys - a teddy bear and a doll made by my grandmother. I still have them both. I slept only with the teddy bear and a real dog or two. The doll has always creeped me out, so I used to lock it in my closet.