It might help to create a more concise letter. The situation is complex and confusing, but just maybe there is a way to break down the letter in a different way.

Maybe try stating is less than 6 bullet points what you are seeking from her and why (briefly!). Maybe follow up a couple of sentences with owning "your" part in things. Don't take responsibility for her bad actions. However it may be best to leave any blame out of your message altogether. Only because it makes her shut down and not listen, not because she is right.

Brevity and clarity may help a lot. The wall of text effect may shut her down.

Hope that isn't offensive for me to say?