Is it ok to consume lactose-free milk (whey protein isolate) in candida diet?

Yes, unless allergic: There are 2 main groups of foods to avoid on a candida diet: sugars (including lactose) & simple starches that feed candida & any foods you may be allergic to. Those with candida often develop allergies to gluten, dairy, eggs, corn, soy, almonds & yeast. If you are not allergic to whey then it's healthy to eat. The best way to tell is to avoid potential allergens for at least a week then try them.