When I read about the distended belly and eating all the time but not gaining weight it took me right back to when my friend's daughter was 18 months old. She looked like the images from Ethiopia during the 90's. Mom spent almost a year fighting for a diagnosis. It wasn't until her child was hospitalized for several weeks at one place and then transferred to Loma Linda (where she spent over a month) that Celiac was discovered. Yeah, her diet is not the same as everyone else's, and my friend has to pack lunches even when lunch is provided, but it it's something they've adapted to quite well. Her daughter is now in middle school and doing great! My friend recently decided she'd try to adapt to her daughter's diet because it seems she may have some intolerances herself.
One thing that is definitely to your benefit is that food companies really have jumped on the "gluten free" bandwagon over the past several years. At first, my friend had to shop at Trader Joe's or health food stores; you should be able to find most of what you need at Stater's or Winco these days.
And I know that this next part isn't the most important, but I'm throwing it out there: Birthday cakes can be made from rice flour, and those meringue cookies make a nice treat. For some reason, those two things stuck out as cause for relief that Kendall wasn't going to be deprived of all the good things in life.
Best wishes in finding the right answer for your daughter and husband. If it is Celiac, once the dietary changes are made, life will be full and wonderful, I promise.
Hugs,
S. :+)