sensitive to brush

My uncles shih tzu get really stiff crusty fur around her mouth and under her eyes, her whole muzzle area. She goes to the groomer but between groomings her face smells. She also has to wait an extra long time for this appointment since the place was booked until May 5th. I tried brushing it but she tries to bite and genuinely hates her face being brushed. I also can't brush her tail, that flips her out even more. So how can I get her face brushed, also should I wet it first, there are little clumps of something stuck in the fur under her chin.

?? Is this food accumulation? Can you wipe her face off after each meal with a wet cloth?

I would try that. some dogs don't like to be brushed.

Well the two clumps under her chin are but is that what makes her face hair stiff? She is not my dog, she's my uncles but I'll tell him to clean her face after she eats.