K.T.
if it's a dairy allergy, lactaid has nothing to do with it. Lactaid reacts with the lactose (milk sugar) and allergies are usually reactions to the milk proteins.
My son is dairy allergic (diagnsed at 6 months) and he was horrible and irritable when i drank milk. Once I stopped eating/drinking all milk products, all was better. You actually have to read ingredients and stay away from any and all dairy, butters, whey, casein, etc. to be able to see if it's really dairy.
try taking out more of the top 8 allergens? ask if you can take her to an allergist. does she have eczema? that was another indicator of allergies for us.
good luck.