This is a common problem with very small dogs who get people food. They rapidly learn that if they don't eat their dog food, they'll get something much better.
You say, "We just give her small pieces". Maybe so, but if you do that all the time, that may be enough to fill up a 6lb dog enough so that she can ignore her own food and hold out for yours! This dog is 5 years old, so she must be eating something or she would be dead by now.
If she likes the canned food, then give her that and stick with it. Switching food all the time makes dogs very finicky. Put it down, walk away and leave it down for 15 minutes. If she doesn't eat it, take it away and offer a new portion again at her next feeding. Do not give her any people food and do not feed her by hand.