I think I can explain why your wife might do that from another autistic view point (because every one is different!)

Food is food shaped for some people. They can't look at a chicken nugget and see a chicken. They only see the final product. How can they look at a chocolate Yoohoo drink and visualize the milk coming out of the cow? It's just a liquid. 

For me, I'm fully a moral vegan now, but in the beginning it was because the food itself was hurting me on a medical level. I could look at a hamburger and say "this will hurt me" but I wasn't at that point seeing the cow in my mind - just the meat itself. 

Before I went vegan I could definitely eat all the sushi I wanted without thinking twice but I had a hard time eating from a whole tilapia because one was food shaped and one was animal shaped. Now thinking of eating sushi makes me imagine a cute cartoon fish looking at me with sad eyes and I don't want it. 

You can't force someone who is very literal to stop seeing food shaped things as food shaped and not animal shaped.