Hi Karen,
Welcome to our internet family. Yes, as you have already figured out, (even though your GI specialist isn't yet quite up to speed on this), MC is similar to Crohn's disease, in that, (as Sara points out), it can affect any part of the GI tract, from mouth to anus, and due to systemic effects, it can also affect most organs outside of the digestive system, as well. Many of us have mouth sores, a few members have signs of esophagitis, some of us have inflammation of the lining of the stomach, (gastritis), and many of us have small intestinal inflammation as part of our MC symptoms. MC commonly involves the ileum, and in some cases, it can be found in the other sections of the small intestine, as well.
Technically, the presence of an elevated lymphocyte count in the mucosa of the duodenum qualifies as a Marsh stage 1 rating. The Marsh scale is a rating scale for damage in relation to celiac disease, which goes from Marsh stage 0, (no damage), to Marsh scale 4, (total villous atrophy). This is exactly the same criteria used in the colon for diagnosing LC. IOW, a diagnosis of LC means that the colon has the equivalent of a Marsh stage 1 rating. Of course, the Marsh rating system is never used in reference to the colon, because there are no villi in the colon. Consequently, the damage in the colon can never exceed a Marsh 1 rating, so it would be pointless to rate it this way. I only mention the Marsh rating system to illuminate why your duodenum is showing exactly the same marker for Lc that exists in your colon. IOW, IMO, your small intestinal inflamation is most definitely related to your LC, whether your doctor realizes it or not.
Regarding deciding between an elimination diet and Enterolab tests:

If you're the type of person who can trust what your body tells you, and act accordingly, and you're willing to keep a detailed diary of what you eat and how you respond, the diet is cheaper. The problem is that even though it's a simple concept in theory, in the real world, sometimes we react just because our gut is so sensitive that it may respond adversely to many foods that it normally wouldn't have any issues with. As a result, sometimes the initial phase lasts for a long time, because we can't always be sure or our reactions, especially if we happen to still be eating a food that we are sensitive to, that we're not aware of.
The Enterolab tests, on the other hand, provide a definitive answer, that's highly reliable, (though not perfect - there are occasional rare inconsistencies, due to the statistical analysis methods used for determining the cutoff points for the test results). They also offer a DNA test that is priced at roughly half the cost of competitive gene tests, that will show you which gluten-sensitive genes you have, and whether or not you actually have a celiac gene, which might be of interest for your kids, and their odds of developing any celiac-type issues.
Again, welcome aboard. You sound like a self-starter, and motivated people get results, so I have a hunch you will soon have your symptoms under control, and you will know more about treating this disease than your GI doc.
Tex