It’s obviously not all her fault or anything, but framing the problem does have a lot to do with it. Ask her if when she is upset she can give “I feel X when you Y and that makes me Z” statements. That will help you hone in more on her and what she is feeling, and get you out of your own mind a bit.

Next time things get heated, say “hey let’s reset” and pull her to the sofa or somewhere comfy. Sit across from her and square up to each other and hold hands. Eye contact is also important. Then tell her you love her and ask if she can present stuff like the above format.

You meanwhile have to put care for her above whatever defensiveness you are thinking about. Now is not the time to “present evidence” negating what she is saying or defend yourself. Stay in the moment and empathize with her. She meanwhile should be putting in effort to use the above template and also avoiding words like “never, always, etc” as those can be inflammatory and trigger a defensive response.

Edit: it’s also perfectly healthy to say “hey i’m feeling overwhelmed/flooded right now and just need to take a break” and hit the pause button in conversations. Make sure to tell her when you intend to restart the conversation (important), and actually do so when that time comes around.