Hi! I know exactly what you are talking about. My son, who is now 20 years old, has severe milk and milk-by-products allergies. More than once he ended up in the emergency ward for an epinepherine shot for accidental ingestion of some food with milk in it (when he was a toddler).
Here's what I learned about Disney....they are wonderful with allergies! When we made our priority seating...I would ask for his milk allergy to be noted. Then, I would ask the waiter at each restaurant to talk to someone about what foods on the menu had milk, butter, whey, etc. in them. Each time, the chief would come to our table and talk with us. Many times they would make a special plate for my son, and use margerine instead of butter, etc. My son always had a very nice meal! Once, at the Brown Derby,they made us a special birthday cake without any milk products!
So, don't hesitate to ask the waiters or the persons behind the counters about the ingredients.....they are extreemly helpful!!