Regarding the letter, SM... what you do with it will be up to you.
Why I say this is, you could finish it and send it to your W before the chat, or not... you could finish it now and send it after the chat... you could wait to the chat to finish it... you could finish it and never send it...
But in the end, if you do end up finishing it, as mentioned, short, concise, clear, from the heart, honest, not focused on her, rather what you have learned, would have done different, etc...
But...
The chat could be a good one... or it could be a bad one... that's up to you... how you listen to what she has to say and whether you react or become defensive...
She asked to chat to you... it wasn't necessarily an open invitation to chat AT HER... even if she asks for your opinion, your best response is that she wanted to chat and anything she says to you, you need to process and think about...
validate, validate, validate... even if you disagree.
Even if she appears positive in the conversation, ANYTHING you say, no matter your good intentions, could very likely be taken the wrong way and could lead to her spewing...
Remember how your last conversations went... do not make the same mistakes...
Be positive... be on your best behaviour... be looking good (but not over done) and well trimmed...
And if things feel like they are going south... KNOW (and practice in a mirror if you have to) what your exit strategy will be... How you can politely and respectfully end things so that you don't risk putting your foot in your mouth...