Nobody wants to look down at the carpet and see dog butt sliding across it. If she's scooting, make a vet appointment.
Anal Sac Problems
Dogs sniff each others' rear ends as a means of communication through scents stored in a fatty substance in anal sacs. These sacs can become blocked or inflamed for various reasons, causing pain or discomfort. Dogs drag their butts on the ground as a way to relieve the problem. Veterinarians may have to lance or squeeze the sacs to relieve buildup of fluids, or may recommend increased fiber in your dog's diet or applying hot compresses to ease the pressure there.
Diarrhea or Constipation
Diarrhea from an illness or from ingesting something toxic or otherwise foreign can leave your dog with a messy bottom. Feces can dry on her fur. Likewise, constipation can cause feces to catch in the fur around her anus. The pulling sensation on her fur may cause her to scoot across the carpet or lawn. Unless there's an infection involved, the simplest treatment is to trim away the soiled fur and wash the area with warm water. A vet's experience is warranted when trimming around the privates.
Fleas and Worms
Fleas are not just annoying for dogs, they are clever enough to infest areas around the butt where it's hard for a dog to bite or lick. When fleas set up around the hind quarters, the itching and inflammation can become unbearable, causing dogs to scoot. Use a flea comb to check for fleas. Some parasitic worms exit through the anus, causing intense itching and discomfort. If your dog scoots occasionally, check her stools and anus for worms.
Severe diarrhea or straining from constipation can trigger a rectal prolapse, which is when a portion of the large intestine protrudes through the anus. This causes discomfort that may lead to scooting. An elongated, fleshy cylindrical mass sticking out from your dog's bottom is a sure sign of a prolapse, and can be dangerous. Call your vet right away and be prepared for your dog to get stitches to repair the problem.