Suggest Treatment For Dry White Patches On The Knees

HEllo..my fourteen year old daughter gets dry white patches of skin on her knees. They get worse if she doesnt put lotion on them, she was putting a perscription lotion on that I had for a skin rash, and it cleared it up. after awhile they come back. If she puts lotion or cream on them, they get better, but then look pink like scar tissue instead of her skin color. What can this be?