Welcome TryingUnderstandHer,
However, my enhanced understanding does not help her.
you underestimate your power. You can't fix her so much is true. Better not to try it either. You and her may not be a natural fit for a close relationship as you have found in the past. But now with your understanding you will be able to reduce triggering her and even more important know how important respect is and take the necessary stands to protect your boundaries. That is quite a lot you can be doing and it can make a huge difference. There are good and bad days in all relationships and with a little precaution we can do a lot to prevent the latter spinning out of control.
Thinking about, you are right understanding won't help her much. What helps are your skills - which takes learning and daily practice.

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