First you’ll want to figure out if it’s truly an allergy, or lactose intolerance, which are two different things. If it’s an actual allergy then she’ll need to cut out all dairy entirely. If it’s lactose intolerance, she can safely eat certain dairy foods, especially in conjunction with lactase pills like Lactaid. And she could eat Lactaid foods for that matter. (They make milk, sour cream, ice cream, etc.) Most hard cheeses, which are aged, have virtually no lactose in them. Things like aged cheddar, Parmesean, etc., while softer cheeses like Brie have a lot more lactose in them and should definitely be avoided. I love Cabot cheddar from VT, which is real cheese that is naturally lactose free. I mention this, because some people who either decide to go vegan, or who are lactose intolerant, and try to go to all vegan options, have a hard time digesting some of the fake cheese products, which can cause as much stomach upset as dairy itself.
After you figure out what the actual problem is, my first piece of advice is to not try jumping straight into fake versions of everything all at once. Try replacing dairy foods with something else entirely. For example, if you usually like sour cream on your chili, try replacing it with avocado, for that cool, creamy texture, without going straight to fake sour cream. Let your palettes forget what those dairy foods taste like, or you’ll be nothing but disappointed with the replacements. You’ll think they taste fake and chemical-ish.
Then, after you’ve been off them for a good long while, try starting with one type of food, say cream cheese. Pick a food that cream cheese really shines in, like bagels & lox, then pick up good bagels, good lox, and 2 or 3 brands of cream cheese, and test drive them. You might find you love the super expensive brand best, or that the cheapo store brand is a nearly dead ringer for what you remember. If you’re worried about ‘wasting’ the ones you don’t like, have a recipe picked out that uses that item in a larger food, like a vegan cheesecake.
I had despaired of ever finding a good fake sour cream, and tried all the big name vegan brands, that people swear by, and hated all of them. Then Kroger, the big grocery chain in our region, came out with one, and I gave it a shot, and LOVED it. It’s half the price of the fancy name brand stuff, and I use it all the time on everything, and in all kinds of recipes. It’s their 'Kroger Simple Truth Non Dairy Sour Cream '.
I’ve tried a lot of fake cheeses, and they never taste like cheese. They usually use lemon or vinegar to create a tang, which always tastes like lemon or vinegar and not like cheese at all. But I did finally find a good one: Treeline Nut Cheese, makes a soft French Style cheese, that is AMAZING. IT reminds me of Alouette. (Not sure if you have that brand in Canada, but it’s a soft cheese, the texture of a whipped cream cheese, that is flavored with things like garlic & herbs.) While I’ve found a few okay fake cream cheeses, I don’t bother with them at all and use the Treeline French style in place of it with bagels.