I'd never heard of it, and a lot of us here probably haven't. I could not find a recipe online, but found references for a balsamic vinaigrette, and a creamy blue cheese. Both apparently healthy.
Good luck. Hope you come back for more than one post.
After doing a Google search, I have come to the conclusion that Witherspoon's is a brand name for a selection of salad dressings, not a particular type of salad dressing.
If you specify the type of dressing, perhaps someone here could provide a recipe.