Firstly, get rid of the treat!
second, put her up somewhere high on a non slip surface and be business like - no high, cheery voice and actions you do when playing. A dog needs to learn to be still and quiet, then have a mad game when all is done. Think about the groomer getting sharp scissors around her eyes, and you will understand why she needs to learn to settle down. Don't be afraid of saying NO (seems to be a dirty word to some people these days! *rollseyes*)
When brushing, tip her head back, holding the the muzzle, brush upwards along the lower jaw, layer by layer (think how a hairdresser works through your hair when cutting or drying it!). One the lower jaw is brushed, work upwards in layers along one side and then the other.
If you still have problems, ask the groomer to show you how it is done.
Tools I use are a slicker brush and then a comb.
'Pedigree indicates what the animal should be
Conformation indicates what the animal appears to be
But performance indicates what the animal is'
Beanara Minature & Giant Schnauzers