Perception and Reality

It's been a long time since I've been on this site.  On the whole, things have been going really well with my wife and I.  This morning I experienced something that I'd like advice on. 

My wife asked me a question this morning, which I answered.  She did not like my answer, and she responded in a louder, annoyed tone of voice with a "you're wrong" tone to it.  Verging on a reprimand.  Anyway, I said something like "You don't need to yell at me.  I don't deserve that tone of voice."  To which she SCREAMED at the top of her lungs "That wasn't yelling.  THIS IS YELLING.  Whenever you don't like what I say, you ....blah, blah, blah." 

Clearly, she was having a bad morning, but I so did not deserve that response.  I am sensitive to yelling, and she knows that.  When I said to her a few minutes later, "You know I don't like yelling.  And when I said I didn't deserve to be spoken to in that tone of voice, you responded by screaming at me.  I didn't deserve that.  If I tell you if feels like you are yelling at me, then you should honor that, not reply by yelling louder!"  To which she replied (loudly) "I was trying to SHOW you what yelling really is."  Sigh.

Clearly, what I initially said to her caused her to escalate.  So, my question is - what might I have said instead when it felt TO ME that she was "yelling" at me that might have allowed her to hear it without responding by yelling even louder?  Or do I just need to suck it up and not be so sensitive?