Did you get the book Crucial Conversations yet? This is the kind of thing discussed in it. This was my ex's way of dealing with unpleasant conversations. He withdrew to keep from having to deal. It used to infuriate me, put me more into the conflict than I had been before because once he withdrew I was left with the original conflict and then, on top of that, trying to figure out how to get him to engage in solving the conflict. We were both reacting in ways that were very counter-productive to solving whatever the problem was.

I think instead of focusing on the fact that she has walked away you need to step back yourself and take a look at how you are choosing to fight your battles. Put some thought into how you can better verbalize how you feel. People withdraw from the verbal battles for a multitude of reasons. She may feel unsafe emotionally to go any further or she may realize that she is wrong and you are right and her pride won't let her admit to it. I'm not so sure figuring out her motive for withdrawing is as important as figuring out ways to discuss the problems that will come up with solutions is.

If she withdraws because she feels unsafe that doesn't mean that the way you are choosing to discuss the issue is wrong, it just means it is being discussed in a way that causes her to feel unsafe. Whatever her reason is for walking off and leaving you holding the bag is immaterial. The important thing is to figure out how to have these discussions in a way that leaves you both feeling like you have been heard and are working toward a solution together.

When an argument gets to the point that one person has walked off, you are both a party to it. You have both had input and you have both acted in ways that didn't get the problem solved. It's not an either or situation and most things in life aren't.

You are thinking that if she would only stop doing this or that things would be better, she is thinking if he would only stop doing this or that things would be better. You both want your sides heard and validated but you are both failing to choose a path that leads to that happening.

When she withdraws from you take it as a sign that the discussion has become dangerous and nothing is going to get resolved at this point. Don't pursue her into the bedroom, don't sit and stew over what you should do next. Take a breather and choose to pursue it from a different path next time.

I caution you this and it's something I had tons of trouble with. Don't allow yourself to feel resentment for her because she has chosen to retreat. Her reasons may not seem valid to you and she could very well be doing it to keep from having to face the issues BUT we all do that when we are not feeling safe to discuss the issues. Bottom line...leaving is something she needs to do and it's a sign that the communication between you to is not productive. Find a better way to communicate.
Cathy