Standing up for yourself is fine. Remember you can have boundaries, you don't have to compromise your values. It is how you enforce those boundaries that matters. Try switching roles in your head and think about a way that she could stand up to you that you would respect her for.
Getting sucked into a fight and angry words is certainly not the way, but yeah I know how hard it can be, I did exactly that this weekend.
I feel kind of selfish putting my schtick out there and I don't offer to ask others how they're doing so please feel free to comment on your own situation here, I wouldn't consider it hijacking a thread, I think we can all learn by hearing about each other's situations and how we dealt with them.
I haven't read about the "going dark" technique (is it in the book), it's kind of hard to do that when you have kids that you share with your spouse, you want to hear about your kids and if necessary discuss them, "going dark" in my situation may make me come off as an unfeeling brute who doesn't care about how his kids are doing plus I like to say goodnight to them every night, tell them I love them, ask about their day, etc. They're too young to pick up the phone and dial themselves so I have to contact my wife to ask her to speak with them (and she does the same when I have them).