So, how do you go about validating while discussing things that you have to move forward on? Things like divorce issues. There's obviously going to be a lot of disagreement, or at least the potential for it. She asked to talk about things last Sunday. a 5 minute conversation could save hundreds of dollars.
It doesn't sound like this discussion is limited to 5-minute topics that will save hundreds of dollars e.g. deciding which parent gets Halloween vs Easter on even years vs. odd years. Then you wouldn't be worried about validating for contentious topics. If she wants to make a proposal, I'd actively listen, then tell her you need time to think about it. Skip any debating, persuading, etc.