That seems like a very short time from their initial meeting to deciding to leave... Is this an exit A? Or is your WW very easily influenced in general?
The e-mail can absolutely be seen as controlling and manipulative. Coaching her on how to distance herself from you is very overbearing.
I have only seen one text from OW to H - it ended 'try not to rage tonight'. I have later realized how manipulative that was, as she knew I thought H was angry at me all the time (he was, out of guilt), but that day he was just coming back from a trip and we had no conflict. She was simply reminding him to be angry at me, but camouflaging it as care.
M 16 yrs, WH62, P54 3 adult blended kids EA 11/13, BD1 6/14 PA fall 14, BD2 2/15 Piecing 2015, BD3 12/15 Separated 4/16 WH moved OW in 5/16 Divorced 6/15/17