I wanted to write to her that although she really hurt me with her lies, deception and insults that I two played a part and that I was sorry that I didn't handle things better and then wish her nothing but happiness.
As Clearmind would say
"what do you hope to achieve by this"
My T asked the same thing more succinctly, "What's the point?"
snappafcw, it sounds like you do know what the point is because:
I wanted to write to her that although she really hurt me with her lies, deception and insults that I two played a part and that I was sorry that I didn't handle things better and then wish her nothing but happiness.
You
CAN write that letter, just like Ironman suggests. You are allowed to share it with us here (just redact all the names) or write it in a journal or somewhere but do not send it to her.
There IS a difference between having the thoughts floating around in your head and putting them down in a concrete form whether handwritten or typed on the computer. Something about the physical act and physically seeing the words creates a neural pattern in our mind that is different from merely ruminating about it. If you feel like doing it, just do it.