Hmm maybe try and make the banister a place she no longer likes. Ie, if you know there is something that she doesn't like then place in on or next to the banister to try and keep her away. Simple but sometimes works.
Good luck
Sorry to hear this! I reiterate what Beaverlaker said, have someone look at her teeth to double check them. Just in the off chance it is something simple like that.
Good luck!