Tim, it's good that you have learned that you need to set the stage. As Dave said we all have the right to discuss bothersome issues and have the right to expect our spouse to be receptive.
I have to wonder why you chose to tell her in the way you did that you wanted this discussion tonight. On the way to work and giving her maybe 12 hours to get her thoughts together? How long have you been contemplating bringing this up to her? Have you had a couple of days to ponder a discussion and now she only has a few short hours?
I think, in your wife's shoes I might have felt a little anxious also. I would have felt hit over the head with it and unprepared. I mean these are big issues!! That's quite the topic to want to discuss and then to tell her you want it that night.
Couples who are in counseling know they have that weekly appointment, that things are going to be discussed and that there is time to put thought into what route the discussion will take. Maybe if you ask her to commit to one or even two nights a week. Plan in advance with both of you having knowledge of what is coming and she won't feel overwhelmed by it.
Am I making sense or am I failing to understand something? Cathy