Hard to tell from those pictures, but she doesn't look too thin to me. In fact she looks pretty much where she should be. You want them lean, and not fat.
I would skip the vitamins, especially if they are made for humans and not dogs. Different species have different nutritional requirements, and if you are feeding commercial dog food, you shouldn't need to supplement, anyway. Also, human product can contain ingredients (like sweeteners) that are harmful to dogs.
I would skip the vitamins, especially if they are made for humans and not dogs. Different species have different nutritional requirements, and if you are feeding commercial dog food, you shouldn't need to supplement, anyway. Also, human product can contain ingredients (like sweeteners) that are harmful to dogs.