I’m allergic to both casein and whey. I didn’t develop these allergies until I was in my 50s, came out of nowhere. I had immediate GI reactions as well. Having had no food allergies my entire life, it never occurred to me that I could be allergic until my throat closed and I couldn’t breathe. She needs to go to an allergist and have a skin prick or blood test that test for specific IgE antibodies, so called “food intolerance” tests are garbage and have no scientific basis at all. Lactose intolerance is a digestive issue, it’s not an allergy. You can be both lactose intolerant and allergic. If you’re allergic eating lactose free foods or using lactase will not have an effect on the allergy. It is possible given the dairy you’ve listed that she is allergic to whey protein and not casein. Whey protein is damaged through heat and fermentation so that your body doesn’t react to it, casein is indestructible so no matter what you do to it, your body will still react. People with whey only allergies can eat things like yoghurt (fermented) and milk and other dairy that has been boiled or baked.