What's a good lactose-free substitute for heavy cream when baking?

In a bread recipe, the cream is just a convenient way to add fat. You can just as well add the water and the fat separately - so change the recipe such that 30% of the weight of the cream is replaced by a fat your friend likes, and 70% by water. If the fat has its own water content (e.g. a margarine), adjust accordingly.

Aquafaba is not at all a substitute for heavy cream. Coconut cream can be used, possibly adjusted for fat content - try picking a brand which is has no additional ingredients such as thickeners. It will give you a coconuty taste and a shorter texture than cream, but this can happen with other substitute fats too.

So there are multiple things you can add (I’m lactose intolerant and bake bread all the time). For recipes that use liquid heavy cream I would use the product on the left which is a nondairy heavy cream equivalent which has both almond milk and coconut cream in it and because of the almond milk that’s added it doesn’t taste quite as coconut-y. The product on the right is an oat milk powder that I use in my bread maker for recipes that call for dry milk powder and is a one-to-one equivalent, I got it on Amazon! Hope this helps ??

Delactose the cream?

I thought this was pretty slick: add lactose splitting enzyme to cream. Maybe a trick to use for other applications too if it works for your friend. Note you have to scroll down a ways in the link.

https://www.fodmapeveryday.com/diy-lactose-free-dairy/

... in the northeast where we are located, we do not have access to lactose-free heavy cream. Now, Monash University has lab tested heavy cream and it is allowed in 1/2-cup (60 g) portions when whipped and they say 2 Australian tablespoons (40 g) as a liquid, but heavy cream is such a common ingredient in baking and cooking that I wanted to learn how to make my own lactose-free heavy cream, knowing that I could then extend the technique to milk, half-and-half, light(er) creams etc.

This writer added an enzyme called lacteeze to the cream. There are photos with test strips showing pre enzyme, no glucose, post enzyme yes glucose so the enzyme worked. They could not tell if all lactose disappeared.

Don’t use coconut cream. It’s a very thick product, completely unlike real cream. “Cream of coconut” is even worse, as it’s heavily sweetened, too.

I use canned coconut milk as a replacement for cream in many dishes, but I haven’t baked with it, so it might have quirks that I don’t know about.

For milk, you can either thin the canned coconut milk, or look for ‘coconut milk beverage’, which is typically sold in aseptic packaging (ie, coated cardboard boxes). It might be in with health foods (with soy milk and similar), but it’s sometimes in the refrigerator section near real milk. It often has gums or other thickeners in it, but I haven’t noticed any problems when cooking or baking with it.