Chanley, lactose intolerance and casein allergy are fundamentally different things, and both very highly documentable.
Lactose intolerance is when your body doesn't produce enough of the enzyme lactase to break down the milk sugar lactose. Instead, the lactose passes through the digestive system undigested and reaches the colon, where bacteria break it down into lactic acid and other acidic compounds. That causes bloating, gas, diarrhea, pain. This is entirely a digestive function and bears no relationship to the immune system.
Casein allergy is similar to other allergies. The milk protein casien passes through the walls of the gut into the bloodstream, where they are attacked by the immune system. IgE produces histamines, which cause an inflammatory reaction. This can result in hives, the lungs swelling shut, stomach cramps or many other symptoms.
Those who proscribe to the Feingold diet for ADD and/or GFCF principles for ASD believe there are non-IgE moderated immune reactions, too. This is, as I'm sure you know, greatly contested in conventional medical circles. But, it's becomming more and more obvious that there are truely non-histemic immune system malfunctions, like celiac disease. It was only a few short years ago that doctors very ferverently believed that celiac disease didn't exist. Now it's well documented, and known to be very prevalent. I've no doubt that the Feingold and GFCF ideas will also have their day...
Anyway, although I said above that casein intolerance can manifest as digestive trouble, the casien intolerance would *not* be managed with LactAid, which is a lactase supplement. So, if the OP was having success with LactAid, then there is no reason to believe that her problem is casien.
Further, a *huge* percentage of the population is known to be lactose intolerant, i.e. 25% of the entire US population, 95% of Asians, 65% of African Americans. Casein intolerance is clearly not even vaguely that high.
Anyway, to address the OP's post, I'd be interested to know if anybody here knows anything about the inert ingredients and stuff in LactAid. Personally, I'm not suspicious of the primary ingredient. Even if it's synthetically derived, it's still a replacement for an enzyme that we would normally produce anyway. It's the "other stuff" in there that potentially worries me. I've taken it occasionally, but I'm only mildly lactose intolerant and prefer to moderate it by keeping my dairy consumption at a lower level, and focusing on yogurt and kefir rather than fresh milk. I've also found that I have no problem at all with raw milk - and I know several other people who've said the exact same thing. My big bugaboo is ice cream. But since I've started drinking raw milk, I have had very little trouble with ice cream, even non-raw ice cream, and even in quantities that would have had me rushing to the toilet in the past. (She says, staring guiltfully at the empty pint of organic Ben and Jerry's Sweet Cream & Cookies sitting next to the moniter...)