Hi there.. upper backpain in kids could be due to many causes like over use ie muscle strain, hard beds/pillows, any spine fractures, congenital deformities of spine, infection of spine, rarely tumors of spine.. I suggest you change pillow and bed and give rest to your daughter's back muscles without dance for a week or two.. if it still persists then please get X-ray done to rule out any spine diseases.. consult orthopedician once..