How Do I Approach My Son & Daughter-in-law About This?

My daughter-in-law (28 yrs. old) heard my grandchildren say that my granddaughters new kindergarten teacher hollars at kids. Now she is up in arms & vows to go to the school before it starts (Aug. 12) & demand that my granddaughter be igned a different teacher. I tried explaining to her that children can hear someone maybe one time raise their voice & then tell it as though the person is always screaming. Yes, I worked in our schools for a couple of yrs. & I have heard teachers raise their voice, but all in all I believe that teachers do care about their students. I have a magazine this month that has an article basically about how to help your child this school year. Also I cut out an article from 6 different teachers giving their suggestions on how to help your child get ready for a great school year. My daughter-in-law is an 'explosive' person so we try to be extremely careful what & how we say things to her so she won't take it out on our son or the kids. Any suggestions?