Making salad dressing without acid or high fat or capsaicin
Acids and spices are generally used to add flavor to the mostly flavorless salad.

To adapt recipes for your relative, you could try:


Use less sauce or dressing. Of cause the fat content of a dressing is high, but if you drizzle just a little bit over the salad, the overall fat content is much lower. Use less sauce to reduce the absolute amount of fat.
Use oils with a strong taste. You'll need much less oil and can greatly improve the taste of a salad if you use oils with a strong taste like sesame oil, walnut oil or peanut oil. 
Add herbs or spices instead of oils. That's how the capsaicin usually gets into a salad, but there are very tasty alternatives: salt, parmesan or a similar grated cheese, oregano, garlic or bears garlic, chives, basil leaves, mint leaves, cress, coriander leaves or finely chopped fennel all add taste to a boring salad without any fat. There are so many more ingredients you could use that the combinations are endless.