perculiar habit of chi

Question
I've always had a 25-30# female dog.
It's my first 6# chihuahua, another love of my life.
However from an early age 6 mos. she would grab her bear, throw it down and as she's laying on her side she was humping the bear. I fear she will do this in her actual mating session.
Have you ever heard of this type of action

Answer
Yes, I've heard of this many, many times and it's something that my own dogs have done and it has nothing at all to do with mating and it's not a behavior that is specific to just Chihauhuas.  The behavior that you're describing is dominance behavior and both males and females can display this.