When I wanted to learn how to stop reacting I would recite the serenity prayer or slogan over and over in my head, before I interacted in any situation and I reminded myself that I was placing principles above personalities and attempting to keep an open mind.
Some key phrases that I used, was: that is an interesting idea, I will think about it or that sounds possible(if it was) or. I understand.
Most important thing to take a deep breath go inside and look for the answers that is good for the unity of both. It takes practice but well worth it.

Thanks for the ideas. Boundaries are still something that I need help with in working my program. If I respond by saying, "I'm sorry you feel that way" (which I have and find it appropriate) then I get the response back- "wow! That's so passive aggressive." Then the guilt sets in. I feel like I can't say anything right and usually will say nothing. When my A is like this, I get the lecture. If I walk out of the room, I get berated. I just want to defuse the situation, but many times I get baited into an argument. This part of the disease is exhausting and frustrating.

The way I understand it, responding doesn't mean that the person won't get all bent out of shape if he or she is determined to get all bent out of shape. (And sometimes they are.)  It's more like "We don't have to attend every argument we're invited to."  So they get all bent out of shape and are gunning for a big argument, but we just stay calm.  So maybe if she says, "That's so passive-aggressive," we say something like, "I don't want to argue.  I'm going to go do [whatever] now."  Sometimes they'll follow us around trying to get an argument out of us, in which case we need plans and boundaries, whether leaving the house, being able to take refuge in a room, or whatever.  If they're going to get all worked up, they're going to do it.  But we can keep from jumping in the insanity pit ourselves.