I have tried this method with the fly spray and hose and it worked well, I assume you could do it with a brush as well. I would use a 10 foot lead rope and let her sniff the brush and then place it on a spot you know she likes to be pet or scratched. (Usually the shoulder is a pretty common safe spot) If she moves away from the brush you keep her circling around you until she stands still. the moment she stands still you take the brush away and praise her. (pressure, release) Keep repeating this, it could take some time. As she becomes more comfortable you can move the brush to other areas, but always returning it to the safe, accepted zone if she looks uncomfortable or about to move off. I use pre-moistened pet wipes to clean her face, nose, eyes and inside her ears. It took her a while to be comfortable with cleaning the ears but by desensitizing her to it bit by bit she grew to love and enjoy it. The faces my mare makes when she is brushed are priceless, lol.