I don't think it's her in all the photos. In fact, I suspect it's not her at all in the photo that jimbo referred to. It's hard to tell, but I believe that is probably a stunt woman - and a really well harnessed one at that. But it is Bella in a few of the photos where the woman is near the bottom of the sheets. The larger versions of those photos clearly show her. And substituting her at least at that point would have been used for closer shots of her climbing down - as well as ones of her coming off of the sheets and onto the ground...
Though IF Bella was up to it, and Burton and the stunt people were willing, I can't imagine that much could have happened to her with all that harnessing...
286 days 12 hours 8 minutes 28 seconds until the day the Depp/Burton DARK SHADOWS is released(ET)!!