Hello Lane McGuffin,
I am sorry to hear of your wife's distress, and your worry and concern.
Quite frankly I'm amazed that a marriage counselor felt this behaviior was normal, so either there's something you're not telling us or the marriage counselor needs a check up himself or herself.
I'm not a professional, I'm not licensed to treat or diagnose schizophrenia or any other medical condition, yet I can tell you with certainty that 18 years is far too long for this to be going on. If your wife does have schizophrenia, she could lack the awareness that she has an illness, and this is a symptom of the SZ called anosognosia, where someone doesn't believe he or she is sick.
Aside from whether or not she has SZ, the fact that this behavior bothers you and has been going on for some time warrants attention and some kind of peaceful resolution. You have written in here for some kind of hope, so that indicates you are not happy with how things have played out.
On the face of things, beliefs such as your wife's could mirror the persecutory delusions of SZ. I recommned you read the Xavier Amador book, I Am Not Sick, I Don't Need Help which will give ideas and techniques about how to approach someone who lacks awareness that she has this illness. If any of what he says rings a bell as true or helpful, you may want to use his book regardless of whether she has schizophrenia or not, as Xavier Amador has also written a layperson's book geared to couples without SZ, I"m Right, You're Wrong, Now What? It is his second book about techniques to break the impasse where one person is convinced of something, or convinced he is right, and the other person is convinced she is right, and they're batting up against each other.
So if you feel you need to suggest your wife see a professional or a doctor about what's going on, I'd start by reading the book, I Am Not Sick to get ideas as to how to couch what you say to her so she is receptive to seeking treatment.
I wish you some comfort and a resolution to this. The process of changing this around won't be quick. It might not be resolved, either, in the way you'd like. The Amador book shows the reader how a person can accept treatment even though she or he doesn't believe there's a problem. That might be the middle point of a resolution that can be achieved.
Again, I don't think this behavior is normal and I'm surprised a marriage counselor would suggest that it is, based on the little you've told us. Your wife needs to be evaluated by a professional, so a second opinion is in order.
Regards,
Christina