I don't think there ever is a time to be ready to let go.
It's such an awful time for you but my motto is, acknowledge how you are feeling, and then try to turn it around and make the most of the time left.

This is a new way to relate to eachother - the next phase in her life. She may be just plain tired of fighting. If you're there to support the 'new' Mom, in her new phase, she'll make it through with peace and happiness, and not a 'fight', but with acceptance.

I envy your bond too.
Enjoy your time together.