Oh, poor baby! The adult tooth most likely broke the baby tooth as it came in. Retained baby teeth are such a problem in toy breeds.
How old is she? Has your vet examined her mouth recently? Retained baby teeth can damage to the adult tooth and even cause infection.
Chinaroad Lowchens of Australia - all about retained deciduous canine teeth
Retained baby teeth are usually removed during the spay to avoid a second anesthesia, but if she's had bad breath for two weeks, she may need a separate surgery.