Dogs lick floors for some reasons that might surprise you. Your dog might be indicating she is nauseated or has an upset stomach. She may have dental problems. She might be stressed, bored or even suffering from mild dementia. Licking the floor is not an unusual problem, and once you understand the cause it's usually easy to stop her from doing this.
Consider the context. If this is a brand new behaviour, chances are there is a medical cause. Dogs who are nauseated will often lick the floor, walls or simply lick at the air. Licking like this is a common symptom of nausea and stomach upset. If anything has changed with her drinking or eating habits, or if her feces has changed consistency, she probably needs a vet visit. A sore tooth or infected gum can also make a dog lick in an effort to relieve discomfort.
Consider her age. Senior dogs can have cognitive dysfunction that causes them to act uncharacteristically or form new behaviors. Teething puppies may also lick the floor or rub their faces, because teething can be painful.
Consider her personality. Dogs can have psychological problems and obsessive-compulsive disorders (OCD), just like people. Licking the floor or licking their feet or flanks can be a mild form of OCD. It can also be brought on by stress, anxiety or boredom. If something has changed in her environment--a new baby, new pet or move--licking may be a stress-relieving behavior.
Rule out medical causes first. It would not be fair to punish a dog for something she's doing because she is distressed or unwell. Take a fresh fecal sample to your veterinarian as well. Bacterial overload and parasites can cause stomach upset. She may need nothing more than a simple worming, and your vet can tell a lot from her stool. Have your vet also check her teeth and gums.
Your vet may suggest a blood panel. This is a simple diagnostic tool that can identify many things like kidney and liver functioning, nutritional deficiencies and even some cancers. It is especially important for senior dogs. If she is healthy but your vet suspects cognitive dysfunction syndrome (CDS), ask about an Anipryl prescription to help keep her calm and focused.
Stress and Boredom
Some dogs are naturally anxious or easily stressed. Others are very hyperactive and without enough exercise and training can become chronically under-stimulated. Floor licking is a common self-calming behavior. Both types of dogs may benefit from more exercise and training. Consider doggie day care once or twice a week. Hire a dog walker, if you don't have time. For dogs left alone, their stress and boredom can be relieved by safe dog chews or interactive dog toys like the Kong (see Resources.)