I think she's whacked. This information is missing from the literature because there is no foundation to it. Milk sugar is found in milk and nowhere else in nature. The sugar in citrus fruits is fructose. You bet she is.
Lactose comes from milk.
But people with LI often have problems with other foods and confuse the symptoms. All that happens is that the lactose, the sugar in milk, is broken down to its parts. This is exactly what occurs in digestion. Your body gets exactly the other nutrients it would otherwise get. If lactase pills work for you, then take them as often as needed.