My two love their grooming... my secret .. treats!! I keep a bottle of different treats on the grooming table, and I must admit they are only good because I bribe them
CoCo has never been too bad, but Coffee, he's another story. Anyway those days are gone thanks to the treats. When grooming Coffee, CoCo actually tries to push him aside so she can have her turn
Try doing just a little patch at a time and give a treat as you begin, and one as you put her down. Try spraying diluted conditioner on the area you want to brush, it brushes easier and does not hurt so much. Hopefully she will learn that brush time is treat time.
I wish you lots of luck. It must be awful to see her so upset.
Sheilagh