Member Rara Avis
Chances are good the shrillness of her voice is at least partially a result of the volume, and chances are even better that the volume is artificial. Instructors are constantly being told to speak louder, usually by someone sitting directly under an air vent. If the class is small enough to be conversational, I would take her aside and admit you are sensitive to high volume. I suspect she would actually appreciate not feeling like she has yell for six or seven hours.
On the other hand, if your company is willing to pay expenses, I might be able to recommend someone with a bit of experience teaching Access.