My unforgiveness is an experimentally verified fact. It's not something I can change by effort of will.

If you won't forgive, Could you simply accept her shortcomings and play to her strengths? Can you identify her strengths?

I might as well quite if I can't rely on her support in a crisis.

Did she not view it as a crisis?

This is the option I am trying to avoid.

do you know why this is not what you have chosen to do?

It's too late to do that now. Anyway, when I'm upset I need support, not a fight.
That is what I am saying - if you start by telling her that you are in a crisis and that you want support in x fashion at this moment and if she can't do x, to please just not make it worse by talking

If you can't be supportive, just shut up." Yes, that's worth thinking about.