If you feel she may be sick you should get her cheked by a vet, if you can. But birds often have white in their droppings, and sometimes they can even be all white. Because of the extra water weight they can't afford to carry in flight birds have evolved to remove uric acid (a waste product of metabolism) in crystal form, not in solution as urine - as we and other mammals do. Birds in effect do not pee. Uric acid precipitated in crystaline form is white. Diet and fluid intake changes, etc, can cause changes in consistancy and color, and so can medical issues, but rest assured white alone by itself may not be an obvious cause for concern. I'm just pointing this out so you will not stress overly much.