D.W.
I think Peg and Helen have hit the nail on the head.
We probably all have nervous habits - hers is just unique compared to what most kids do at that age.
We noticed recently that both of our kids stick their tongues out when they're really concentrating on something. Do we bring it to their attention? We don't think so, but we also don't want them to be teased about it.
Our son still sucks his thumb like Helen mentioned (he's 3.5). Our daughter will be 2 next weekend, and we're having a heck of a time getting rid of the pacifier despite it having affected her teeth already.
I had a friend in college who had to have a piece of lace to rub between her fingers when she was nervous. I used to finger spell (sign language) everything I said and heard on the radio/TV.
I would mention it to the pediatrician just in case it's not as uncommon as it seems and may indicate other behavior patterns. But, I wouldn't blame yourself or the environment in which you are bringing her up. It may just be part of her DNA to soothe herself, and this is the way it manifests itself.