hi,read ur problem, speaking kindly but firmly to her may be the first step.Find out if she does have a genuine problem ,at home,or workplace and finally psychological.Also a gentle reminder of her responsibilities may not be out of place.Once convinced that despite ur efforts there is no response or improvement, a graded response may be resorted to.A recorded counselling, failing which disciplinary action under the powers vested on u as her superior.Remember indiscipline tolerated for long or ignored will have very a bad effect on the rest of the team,aswell as undermine ur authority.Even if ur problematic employee is brilliantly gifted and professionally sound ,such qualities may have to be sacrificed at the alter of organisational interest and teamwork