People with lupus should definitely stay away from any alfalfa products, including alfalfa sprouts, because they contain an amino acid called L-canavanine, which can cause lupus flares. All the lupus experts pretty much agree on that one. Other kinds of sprouts don't have the same levels of L-canavanine, but you might want to avoid them anyway. And some of the rheumatologists recommend avoiding foods or supplements that are high in zinc because it stimulates the immune system - which is exactly what you don't want in lupus. Some of the herbal cold remedies contain zinc. And a lot of herbal products contain echinacea or goldenseal, which people with lupus should also avoid.
As for dairy and soy, like you, I've read a lot of conflicting information - none of which seems to be based on independent research. Soy is definitely a common allergen, but most true "food allergy" develops in childhood in people who have other allergies too. So I'm not sure why they recommend avoiding a food that's an allergen if you're not allergic - kind of like telling people not to eat peanuts because they are a common allergen too.
I know some books say to avoid soy, other say to avoid wheat and gluten, others say to avoid nightshade plants like tomatoes and potatoes. You can read 15 different books, and all of them will have a different program or protocol that's guaranteed to help. But lupus patients have such a wide range of symptoms, and no one really knows how much the disease outcome is influenced by genetics and heredity, so no one diet will probably be right for everyone. Since heart disease is a big risk for women with lupus, following a sensible, heart-healthy diet may be your best option.