I was going to say the same thing. Perhaps she has a sensitivity to loud noises, not neccessarily the arguments or tone of voice. What if you are loud because you are happy/excited? It is quite common for little ones to have problems of one sort or another with their ears so maybe get it checked out?

I am guilty of "flying off the handle" and raise my voice more than required. Just tonight I noticed DD looking at my face while I was "talking" to dh in another room. She was just assessing my expressions to see if it was anything to be concerned about and then she happily went on with her play. We often raise our voices when trying to make ourselves understood but we rarely have a full-on argument, expecially in front of her.