Keep it simple and to the facts.. don't add anything, let the ex or lawyer do the legwork.
Stick to email and respond only with the facts, no emotional issues.
Take accountability for the time you have with your daughter. Know her vacations, half days and plan accordingly.
Do not expect your ex-wife to be a problem solver at this point. She has to be the one to offer.
Any suggestions you make will look like demands. Facts, only bare bone facts.
You are a single parent when you have your daughter.. think like one. Turn to friends, trusted neighbors and family. Call the school when you're not sure of schedules and ask questions. They love to help nice daddies.