Don't respond about the letter, it's words, you need to see actions, not even worth acknowledging.
Go do what you need to the car, no need to tell her, just go do it. What do you want the living arrangements to be, don't address it as a discussion, tell her (I thought you already did) what you want.
M - 9 1/2 years 5/5/16 - Bomb drop - 3 week EA 10/31/16 - We sold house 01/10/18 - D Finalized