Butt scooting usually means worms. My dogs have done that on a occassion but nothing was wrong with them. Is it after she goes to the bathroom or before? Sounds like she could have a "DingleBerry" maybe wiping off. If she does it again maybe use some toilet paper and wipe her hieni. There could just be some irritation in that general area and the carpet makes it feel better. If she does it outside in the grass she could get ring worms. I would just treat the area with moisturizer or neosporin. Maybe the irritation will clear up or otherwise you just have a very strange and unique cat