The nibble, nibble, nibble gives her something to do while she's discovering that not only does brushing feel nice, but she can hold still for it, too!
When you've got her good with you, then start having others run the brush over her.....even just 1 light stroke is good to start, with you standing in front of her with the nibble, nibble, nibble treat. You can phase out the treat quite easily once she is more comfortable with the whole thing.
I think at five months Chili was still trying to kill the brush, LOL! She passed her CGC at 8 months. It's hard for the puppies to hold still!