Wow, you're missing the big issue here as you focus on this tiny (but yes, INTENSELY annoying) issue.
Big issue: "The woman is so moody and bitchy a lot of the time that it's like walking on eggshells around her." And you are "afraid of what I might get" if you speak up. Your own words, and very telling.
If you're afraid to discuss this with her and are already on eggshells at work, frankly, she's a toxic boss, or at least a pain of a boss. She would have to be a complete goddess in other ways to make this tolerable. I'd bet there are other issues with her that you're not mentioning here, since you're focused on the e-mail problem. But step back from that one thing and look at the big picture. I'd be looking for a transfer to another office if there's any way to do it, or for another job.
It totally rots to work for someone who keeps employees on edge and who is bitchy all the time. Get out. If you're saying to yourself, I can't get out -- at least start trying, now. If you put off looking, you'll end up working for her ever longer; why not at least start to hunt?
There is more than e-mail etiquette at stake here; do you really want to work for this boss even if she DOES clean up her act about the e-mail and stop doing it out loud?