1/16". That is the distance one has to move one's pinky in order to not to sound like an idiot. I try not to be judgemental generally speaking, but if you email me in all caps I will think you are stupid. Turn off that caps lock, and suddenly you will rise a great deal in my esteem.
I wouldn't even read someone's email written to me in all caps, on the basis that I have never seen anything written in all caps that was worth reading, back when I would actually read text written by troglodytes. I no longer waste my time.
I know this sounds harsh, but there is no excuse for writing in all caps. None. Ever. If one can't use the shift key (and it's possible that someone could find themselves in this situation) then type in all lower case. I have zero problem with an all lower case email. I will read it, and not think the sender is dumb at all.
Previous posters have given you great links for giving her information. I wanted to post because your employee (you are her boss, I gather) makes herself and everyone she represents look like morons. Yes, it is a big deal. Who knows how many recipients of her emails feel as I do?