While I know this isn't the best word to use, I would make the e-mail more "dictating" (IOW tell her what you will be doing)
W: When you lost your job last year we had a conversation and the conclusion that we both agreed to was I would be maxing out my FSA. It violates the federal and state tax laws for two people to claim the same dependant despite the filing status. Please adjust your plan and withholding accordingly.
Your W has proven time and time again she doesn't care "how things work". Her goal is to get as much money as she can from you no matter what. If she does not comply with adjusting things then include this in her settlement offer. She has refused to communicate on just about everything then informs you after the fact (your daughter's schooling, daycare, dr's appts and so on). Don't expect something different by doing more of the same. She was very comfortable demanding you pay this or pay that. This is not a demand, it's a fact of how things will be. Period.
