Letter writing is a great way to overcome the emotional turmoil of in the moment disagreements. It allows you to be truthful as well as thoughtful without the emotion induced brain fog, accusatory declarations and defensive degradation.
I agree with the sleep on it before you give her the letter advise as well.
Ask her to write you a response and afterwords you can both discuss from a more enlightened platform.
It is the emotional responses that kill reasoned discussion in a marriage. I think anyone who has been married can understand this point.
Letter writing is a great way to overcome the emotional turmoil of in the moment disagreements. It allows you to be truthful as well as thoughtful without the emotion induced brain fog.