Groomer Troubles and Thyroid Issues

Hi! I have a 9-year-old cat who has never had any behavioral issues, but is a calico so generally has some type of small attitude every day (lol). She is gentle around people but can sometimes be a bit of a bitch to her sister. Recently, she has been shedding constantly and has lots of dander, so I scheduled her to go to a groomer. While I wasn't expecting her to be sunshine and rainbows, she attacked one of the groomers pretty badly at the beginning of the groom and got sent home. I felt horrible about it. The groomer also told me that her thyroid may be out of wack because of her shedding and dander. She also mentioned that might be why she was aggressive, and now I'm worried she is sick. This cat is 16 pounds, so I don't think it's hyperthyroidism, but I'd love to know if this groomer is on the right track or if I'm being anxious for no reason? I have a vet appointment lined up in a few weeks, regardless.