Severe Pain Due To Kidney Stones. Discharge Of White Sand Like Substance Through Urine. Does She Have To Go To A Nephrologist?

My grown daughter (age 23) has had kidney stones for 5 years. She has passed many stones in those 5 years. This weekend she experienced the worst pains she has ever experienced. She began passing a white, think sandlike substance for several days She would experience horrible pain and pressure and then push and the substance would release in clumps. I am very worried about her . We have made an appointment at her urologist , but not expecting anything because they rarely have any answers for her. I was wondering if we should consider going to a nephrologist instead of a urologist. I am beginning to think we may be dealing with something in addition to kidney stones. Do you have any ideas of where we should turn at this point.