I had the same kind of difficulties with my wife. A small bowl of breakfast cereal, or an evening dinner, would take 3/4hr each to get through, if indeed they were ever finished. She would refuse to open her mouth, push food out with her tongue, nibble food, store her tablet medication in her cheeks and spit it out when she thought I wasn't looking. She often put her fork or spoon down shortly after starting eating and effectively gave in (I believe she found it very tiring trying to remember what to do with them, etc.). After dropping from size 18 to 12/14, and for other reasons, she was put on Metazapine which can have the side effect of encouraging appetite. She was only on Metazapine for 4wks (taken off because of a suspected adverse side effect) but since that time has got back to her usual normal healthy eating and has regained some of her weight loss. That was probably 12months or so ago and she is now just starting doing some of the same things again!
In total innocense and lack of knowledge that there was such a condition, I have refered to her as 'like a hamster' to our sons when describing what she has done (I have also said she was like a magician). Indeed, today she spat out a prune stone when I was getting her to clean her teeth. She is a little constipated on her new medication and I put some prunes (supposedly pitted) on her cereal yesterday morning. Since then we have had lunch, fruit and drinks in between meals, dinner comprising main course and sweet, bedtime drink, night medication and water, slept for 7hrs, breakfast cereal (no prunes) and tea, and tablet medication this morning and through all this she has managed to tuck that prune stone in her cheeks!! At times I suspected something was wrong but despite my best efforts she defeated me.
Her dietician suggested high protein food, creamy yoghurt, ice cream, double cream, condensed milk, etc., and also suggested bright single coloured plates, bowls, as an aid to focussing attention on the food. Hope you soon manage to get the problem sorted in everyones interests.