probably mean her anal glands need to be expressed if it's happening a few times. You should go to your vet. It could maybe also be tapeworms but you'll would have seen them in her stool before the scooting.
If it's just a one time thing, could be just an itch .
Our puppy was dragging her bottom, so we took her to the vet for an exam/to have the glands expressed. Not much came out of her glands, and it turned out she just had an irritation kind of like a diaper rash. The more she scooted, the worse it got. Our vet thought the irritation came from some loose stools. She advised us to put Aquaphor on her bottom for a few days, and sure enough that did the trick. However, we never would have known it wasn't the glands if we hadn't taken her in, so I think it's important to have your dog vetchecked if they're scooting. It cost us $40--$20 for the exam and $20 for the draining even though it didn't result in much.