You handled it fine. Next time, maybe throw in a validation preface, such as:
Her: "Wow, that really hurts, you didn't remember me."
You: "I'm sorry, that's certainly not my intention. Look, I gotta run, I was just headed out the door. I"ll talk to you later -- bye!"
but other than that, I'd say you handled it perfectly.
Remember, this feels wrong because of your INSTINCTS. And your instincts, frankly, HAVEN'T GOTTEN YOU WHERE YOU'VE NEEDED TO GO.
DBing IS COUNTERINTUITIVE. It WILL feel wrong at many points.
The other "mistake" you're making -- or I should say the other way you're reading this wrong -- is that you're judging "success" by how she reacts, SHORT-TERM. Specifically, how she responds to you right at that moment.
I'd encourage you to begin, if you haven't already, to judge your success two ways:
1. By "Did I do the right thing?" and
2. OVER TIME, is she making a move back toward the marriage?
The problem most newcomers have -- hell, the problem most VETERANS have -- is that we quickly ditch #1 in the face of a short-term negative respond to #2: we "blink."
As Gucci suggested, go and read Pearlharbor's old threads. Her boyfriend did NOT immediately respond to what she was doing, not in any good way. But OVER TIME, it WORKED.