Yorkie Grooming Please Answer?

My yorkie is going to get groomed on June 2nd, it's her third time. She has so many ratty knots. I tried to brush her, but she wouldn't let me, & I rather not fight with her. Is she going to be shaved? I really hope not, but her sister did get shaved when she had all those knots. So, what should i do? Should i ask the groomer not to shave her and cut the knots out?