Good afternoon Deb,
I'm Doug, and I'm very sorry to hear of your situation. My goal is to provide you with excellent service today.
You asked: If I write a document myself and we both sign it and have it notarized will that stand in a court of law? Also, do we need to file that document with the courthouse in the county we reside in? No, that kind of a document will not be enforceable in court.
As your daughter is an adult, unless one or both of you have been appointed as your daughter's Legal Guardian, then she is deemed competent and whatever either of you convince her to do is up to you. A contract between you as parents will not change that fact.
What needs to be done is that you and your ex need to petition the Probate court in the county where your daughter resides to be appointed as her joint Legal Guardians and then you can ask the court as part of the order to mandate that there be discussion between the two of you when it comes to medical care and other major life decisions.
You may reply back to me using the Reply link and I will be happy to continue to assist you until I am able to address your concerns, to your satisfaction.
I hope that I have been able to fully answer your question. Please be so kind as to rate my service to you. That is the only way I am credited for assisting you.
I wish you and yours the best in 2016,