Ideally, find your professor during office hours, and say something like "Hey, this has been confusing me... I'm seeing all these references to one pronunciation and you've been using another. Is there a disagreement in the academic community, or are both pronunciations valid, or did the author use a less-common pronunciation, or are these other references simply wrong?"
In other words, don't tell her that she's making a mistake; ask her to help you learn. Much more polite, much harder to take offense at, and much less likely to embarass you if she says either "Well, this is how [author] always pronounced his name when I spoke to him" or "I have a slight speech impediment that I'm a bit embarrassed about; thanks for not bringing this up in public."
The fact that she's outvoted does not necessarily mean she's wrong. For that matter, she may not be aware that there is a difference, or not be able to reproduce that difference accurately, if her accent isn't the same as the others you've spoken to (or your own)... or you may be having the same problem in the other direction.
You have an interesting question. Ask it. In private, and as a question, and you'll probably get an interesting answer and maybe a bit of an uptick on your grade for having made additional effort. If you tell her that she's wrong, and/or do so in the middle of class, it's likely to go less well for either of you.
If you really can't meet with her before the exam, despite your best efforts, you have to decide whether you're going to pronounce it her way, pronounce it your way and -- if challenged -- say "I've been meaning to ask about that; this is how I've always heard it...", or try for a compromise between them with the "I've been meaning to ask" as a fallback.
But I really doubt you're going to get dinged for getting this wrong if you get the rest of the exam right. So maybe you should focus on aceing the exam, rather than on this nitpicky point.