Our Rottie also suffered from hot spots and malamum's advice is spot on. The area needs to be kept as dry as possiable and this is difficult as you can not get near her to treat her. They can spread like wild fire, start off a small patch and within hours your looking at a huge sore. We found with our dog that it was food that brought his on, anything with preservitives in it. We cut out most meat products and fed Bonnie Dry food (made with Kangaroo meat no additives or preservitives) and vegies, pasta, rice, eggs and yoghurt etc.
This helped him, when he had a flare up we would scub with iodine dab dry with guaze and apply anticeptic powder or cream.
I know this is not of much help as you cant get near her. Is someone able to distract her with food whilst the other person gets some powder on her back. Maybe if she relises that you arnt going to hurt her she may relax a little. Start of be just tring to get near her and praising her for that.
Good luck.