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.
Yogurt comes in low-fat variations and in my experience they work pretty well.
Yogurt can be used as a dressing. In a lot of instances you can make a nice dressing just by taking the recipe of a mayonnaise based dressing and then replacing the mayonnaise with yogurt. (I don't mean it will taste the same, just that the recipes will produce a still nice but ...
I don't know whether the "ranch mayonnaise" you had was a commercial product or simply something the supermarket whipped up to put on sandwiches. I personally had never heard of "ranch mayonnaise" as a supermarket product, but an internet search tells me that apparently some companies do market it.
In any case, both the dressing and mayonnaise are likely ...
You can work with sweet and salty tastes. A cold soy sauce and mirin/honey mixture is sure to add some good flavours to a salad.
You can also crush garlic and ginger, fry it up, then add soy sauce, honey/sugar/mirin and a corn starch slurry for a teriyaki style sauce you can dress your salad with after it's cooled.